The Quality of Greek Islands’ Seawaters: A Scoping Review

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The present study critically reviews the quality of the current status of the seawaters of Greek islands and brings their unique environmental potential and potential threats to the surface, indicating the need for continuous monitoring of not only in terms physicochemical parameters but also tracing potential contaminants and emerging threats in order to sustain the environmental health of these waters.

Abstract

Background: Greek islands face mounting pressures on their marine water resources due to tourism growth, agricultural runoff, climate change, and emerging pollutants. Safeguarding seawater quality is critical for ecosystem integrity, public health, and the sustainability of tourism-based economies. Objectives: This scoping review synthesizes and evaluates the existing research on seawater quality in the Greek islands, with emphasis on pollution sources, monitoring methodologies, and socio-environmental impacts, while highlighting the gaps in addressing emerging contaminants and aligning with sustainable development goals. Methods: A systematic literature search was conducted in Scopus, Google Scholar, ResearchGate, Web of Science, and PubMed for English- and Greek-language studies published over the last two to three decades. The search terms covered physical, chemical, and biological aspects of seawater quality, as well as emerging pollutants. The PRISMA-ScR guidelines were followed, resulting in the inclusion of 178 studies. The data were categorized by pollutant type, location, water quality indicators, monitoring methods, and environmental, health, and tourism implications. Results: This review identifies agricultural runoff, untreated wastewater, maritime traffic emissions, and microplastics as key pollution sources. Emerging contaminants such as pharmaceuticals, PFASs, and nanomaterials have been insufficiently studied. While monitoring technologies such as remote sensing, fuzzy logic, and Artificial Neural Networks (ANNs) are increasingly applied, these efforts remain fragmented and geographically uneven. Notable gaps exist in the quantification of socio-economic impact, source apportionment, and epidemiological assessments. Conclusions: The current monitoring and management strategies in the Greek islands have produced high bathing water quality in many areas, as reflected in the Blue Flag program, yet they do not fully address the spatial, temporal, and technological challenges posed by climate change and emerging pollutants. Achieving long-term sustainability requires integrated, region-specific water governance linked to the UN SDGs, with stronger emphasis on preventive measures, advanced monitoring, and cross-sector collaboration.

1. Introduction

The Mediterranean basin ranks among the world’s most prominent tourist destinations, with its islands attracting substantial attention due to their rich historical, cultural, and natural heritage [1]. While tourism provides significant socio-economic benefits, it also exerts considerable pressure on coastal and marine environments, which are already impacted by concentrated human activities such as urban expansion, industrial discharge, and maritime traffic [2]. Growing awareness of the adverse environmental impacts of tourism, coupled with the need to balance social and economic considerations, has underscored that the objective of achieving truly sustainable tourism remains largely unmet [3].

Water quality is of paramount importance for environmental, economic, and public health reasons. Contaminated water can transmit pathogens that cause diseases such as cholera, typhoid, and dysentery [4]. Furthermore, clean and safe waters support ecosystem health, including the productivity of fisheries and the maintenance of biodiversity [5]. Recreational activities such as swimming, boating, and fishing rely heavily on good water quality, and degraded conditions can deter tourism, resulting in economic losses for local communities [6]. These interconnections highlight the importance of safeguarding water resources, particularly in regions where tourism and coastal livelihoods are deeply intertwined [7].

The Greek islands present a unique combination of environmental and socio-economic characteristics that make water quality management both critical and complex. Ecologically, they host high levels of biodiversity, including numerous endemic plant and animal species adapted to insular environments [8]. Many islands contain sensitive habitats such as seagrass meadows (Posidonia oceanica), coastal wetlands, and marine protected areas [9]. Socio-economically, the islands experience high seasonal population fluctuations due to mass tourism, resulting in sharp increases in water demand and waste generation during summer months [10]. Geologically, they vary from volcanic (e.g., Santorini) to limestone formations (e.g., Corfu), influencing hydrology, aquifer vulnerability, and pollutant mobility [11]. They are also vulnerable to natural hazards, including earthquakes, droughts, and coastal erosion [12]. This combination of ecological richness, tourism intensity, and environmental vulnerability underscores the need for integrated, science-based water quality management strategies [13].

The Greek islands are characterized by exceptionally high biodiversity, including numerous endemic plant and animal species; large seasonal fluctuations in population due to mass tourism, which places intense pressure on water and waste management systems; and high exposure to natural hazards such as earthquakes, coastal erosion, droughts, and wildfires [14]. They face challenges from tourism, urban expansion, and climate change, leading to natural hazard susceptibility, particularly in coastal areas, with significant infrastructure at risk [12,15]. Furthermore, genetic studies on indigenous species from the Greek islands reveal a severe loss of genetic diversity due to declining population sizes and the introduction of alien species, emphasizing the impact of socio-economic factors and geographic isolation on these unique island breeds [16]. These characteristics highlight the intricate balance between natural heritage, tourism development, and environmental conservation efforts on the Greek islands.

Nutrients play a crucial role in ecosystem dynamics, influencing the growth of algae and aquatic plants, which can lead to eutrophication and water quality degradation [17]. Contaminants, such as persistent organic pollutants (POPs); heavy metals; pesticides; and compounds from the agri-food industries, olive mills, breweries, and wineries, are widespread in such local environments, posing significant environmental risks to water quality and health risks to populations [18]. Additionally, the availability of elemental nutrients like nitrogen and phosphorus can impact infectious diseases in autotrophs, creating bidirectional relationships between disease and ecosystem nutrient dynamics [19]. Ultimately, rising nutrient loading due to urbanization and sewage effluents can have detrimental effects on aquatic ecosystems and human health, emphasizing the need for holistic nutrient mitigation strategies that consider both terrestrial and marine environments [20].

In recent decades, the pressures on the marine environment of the Greek islands have been intensified by agricultural runoff, urban wastewater discharge, maritime transport, and the emerging issue of microplastics and synthetic contaminants, such as pharmaceuticals and PFASs [21], heavy metals, antibiotics, polycyclic aromatic hydrocarbons (PAHs), and organophosphate esters (OPEs), in marine environments [22]. These threats are compounded further by climate change, which is expected to increase sea surface temperatures, alter precipitation patterns [23], and intensify extreme weather events, affecting their health and immune systems, leading to potential antibiotic resistance in bacteria like Vibrio spp. [24].

The research on the quality of marine and fresh waters in the Greek islands underscores the environmental and economic interconnectedness of these waters. To evaluate water quality, multiple factors such as physical, chemical, and biological indicators must be considered. It is essential to comprehend how these parameters are influenced by natural processes and human activities. This study offers a thorough examination of the current state of the water quality in the Greek islands, concentrating on the difficulties and potential solutions and mitigation approaches to preserving and enhancing the ecological integrity and sustainability of these critical water resources. In Figure 1, the geographic extent of the study area, showing the Greek islands and the main island groups considered in this scoping review, is illustrated, with the blue shaded area delineating Greek territorial waters.

Given this complex interplay of environmental and socio-economic factors, safeguarding seawater quality requires an integrated, evidence-based approach. Effective management must combine robust monitoring of physical, chemical, and biological parameters with advanced tools such as remote sensing, artificial intelligence, and citizen science. Equally important is aligning local and national strategies with global sustainability frameworks, particularly the United Nations Sustainable Development Goals (SDG 6: Clean Water and Sanitation; SDG 14: Life Below Water).

This scoping review synthesizes the current research on seawater quality across the Greek islands. It identifies key pollution sources, assesses the monitoring methodologies, examines environmental and socio-economic impacts, and evaluates the adequacy of the current management responses. By highlighting both achievements and gaps, this study aims to inform targeted interventions and support the long-term sustainability of these ecologically and economically significant waters.

2. Methods

This scoping review was conducted in accordance with the PRISMA Extension for Scoping Reviews (PRISMA-ScR). A completed PRISMA checklist is shown in Figure 2. This scoping review followed the PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines, which provide a structured framework for identifying, selecting, and synthesizing the relevant literature, as put forward by Tricco et al. (2018) [25]. PRISMA-ScR was chosen to ensure methodological transparency and reproducibility and to minimize selection bias.

Literature searches were performed in Scopus, Web of Science, PubMed, Google Scholar, and ResearchGate. The search strategies were developed in consultation with previous scoping review methodologies (Arksey & O’Malley, 2005; Levac et al., 2010) [26,27] and adapted to each database using Boolean operators and relevant keywords.

Figure 2 illustrates the study identification and selection process. The initial database searches yielded 510 records. From this total, 65 duplicates were removed, leaving 440 unique records. From this total, 199 records were eliminated based on the title and abstract, leaving 221 records to be retrieved for full-text review. During the full-text review, 43 papers were excluded due to the wrong region or the wrong publication type, leaving 178 papers to be included in this review.

Scopus, Google Scholar, and ResearchGate were utilized to find scholarly articles, focusing on articles published within the last 2–3 decades and written in English or Greek, with the following search keywords employed, in combination with the terms “AND” and “OR”: “water quality”, “islands”, “Greece”, “emerging contaminants”, “contaminants”, “pollutants”, “emerging pollutants”, “water contamination”, “water pollution”, “effect of water contamination”, “nutrients in seawater in Greek islands”, and others (beyond the initial keywords, additional relevant terms were identified and organized into thematic categories for better navigation). Keywords such as “gulfs”, “basins”, “lagoons”, “bays”, “beaches”, and “coastal areas” were excluded. After meticulously evaluating the results, reliable and relevant sources were chosen, prioritizing those published in reputable journals or by recognized researchers. This ensured a comprehensive review covering a broad spectrum of water quality topics in the Greek islands.

Relevant data from the included studies were extracted and categorized based on

• The type of pollutants or contaminants studied (e.g., nutrients, heavy metals, microplastics, emerging contaminants);
• Geographic location and island group;
• Water quality indicators measured (e.g., salinity, pH, chemical oxygen demand);
• Monitoring or assessment methods used;
• Key findings and implications for public health, tourism, or ecosystems.

As this was a scoping review, no formal risk of bias assessment was conducted, in line with the PRISMA-ScR recommendations.

3. Results

3.1. Water Quality Parameters

Surface water quality assessments involve the evaluation of numerous physical, chemical, and biological parameters. The physicochemical parameters commonly analyzed include pH, temperature, dissolved oxygen (DO), salinity, conductivity, total dissolved solids (TDSs), and biochemical oxygen demand (BOD) [28,29]. Chemical parameters such as the major ion concentrations (e.g., Ca²⁺, Na⁺, Mg²⁺, K⁺), bicarbonate ions (HCO₃⁻), and various anions (e.g., Cl⁻, SO₄²⁻, NO₃⁻) are crucial indicators of water quality [30,31]. According to Ladakis et al., nutrients in the North Sporades Islands have been found with mean concentrations detected of 0.03 μmol of N/L NO₂⁻, 1.25 μmol of N/L NO₃⁻, 1.11 μmol of N/L NH₄⁺), and 0.12 μmol of N/L PO₄³⁻. In the same study, heavy metals were quantified as having mean percentage dissolved concentrations of 60% for Cu, 82% for Zn, 92% for Ni, and 80% for Pb. The authors mentioned that the anthropogenic impact is low for Cu, Zn, Ni, and NH₄⁺ concentrations. The influence of seawater from the Black Sea is evident in the North Sporades area.

Biological parameters like the presence of specific microorganisms and the biochemical oxygen demand for five days (BOD5) are essential for assessing water contamination levels and suitability for consumption [32]. Additionally, water quality indices (WQIs), irrigation water quality indices (IWQIs), and statistical methodologies such as a discriminant analysis (DA) and multivariate statistical approaches (MSAs) are employed to provide a comprehensive evaluation of surface water quality, aiding in the decision-making processes for water resource management and protection.

Additionally, bacterial contamination significantly impacts the health of marine ecosystems by contributing to the deterioration of coastal environments, affecting essential ecosystem services provided by bacteria, and potentially leading to the spread of infectious diseases. Bacteria play crucial roles in marine ecosystems by regulating nutrient cycles, synthesizing vitamins, and degrading contaminants, making them vital indicators of ecosystem health [33]. Aquatic ecosystems, including the Mediterranean Sea, are increasingly threatened by emerging contaminants like antibiotics, microplastics, and heavy metals, as well as the compounds present in agri-food bio-waste, which can be transported in surface and seawaters. All of these types of contaminants can lead to serious consequences for the quality of the microenvironment of surface water and seawaters on a local basis for each Greek island, further affecting both marine organisms and human health [34,35].

Finally, heavy metals significantly impact seawater quality by posing threats to aquatic ecosystems and human health. Studies have shown that heavy metals like Zn, Cu, Cr, Ni, Hg, As, Pb, Cd, Fe, and Mn can accumulate in water bodies due to various sources, such as industrial activities, mining, and atmospheric deposition [36,37,38,39].

Studies have been conducted to assess water quality using various indices, such as the Hellenic Water Quality Index (HWQI) and the Canadian Council of Ministers of Environment Water Quality Index (CCME WQI) [40]. Monitoring efforts have been enhanced through a combination of Earth observation data and in situ measurements to assess water quality, particularly focusing on trophic status prediction [41]. Furthermore, historical perspectives highlight the evolution of water quality management in Greece, emphasizing the importance of potable water quality for public health and life expectancy improvements [42]. Overall, these studies underscore the ongoing efforts to monitor, evaluate, and improve the water quality of freshwater sources in Greece, providing valuable insights for sustainable management practices.

The primary sources of pollution affecting surface water quality in Greek islands are predominantly linked to agricultural activities, such as the cultivation of crops like cotton, corn, and wheat, leading to significant nutrient load discharge [43]. Additionally, inadequate wastewater management practices, including untreated wastewater discharge, contribute to the deterioration of water quality, highlighting the importance of achieving Sustainable Development Goal 6.3 to reduce untreated wastewater discharged into the environment [44]. In Greek islands, measures to mitigate threats to surface water quality include the implementation of monitoring programs to assess pesticide pollution from agricultural and urban sources [40,45]. Additionally, efforts have been made to address water quality issues by focusing on the physicochemical quality of rivers through the use of water quality indices like the Canadian Council of Ministers of Environment Water Quality Index (CCME WQI) [46]. Furthermore, in response to the challenges posed by climate change, strategies have been proposed to manage and protect water quality, considering factors such as eutrophication, emerging contaminants, and climatic variability impacts [47].

3.2. The Geographical and Hydrological Characteristics of the Greek Islands

The Greek islands exhibit significant geomorphological diversity, characterized by limited freshwater resources and increasing demands for sustainable water management. Greece comprises over 6000 islands and islets, of which only 227 are inhabited [48]. The geomorphology and hydrogeology of these islands vary considerably due to their complex geological structure and climatic heterogeneity. Most islands suffer from water scarcity, while escalating water demands—primarily driven by tourism and the arid Mediterranean climate—underscore the critical importance of sustainable water resource management.

The pronounced mountainous terrain of many islands, combined with their limited geographical extent, hampers the collection and storage of surface water. Rapid surface runoff and the absence of extensive lowland areas inhibit the formation of large natural reservoirs and aquifers. Additionally, several Aegean islands are of volcanic origin and composed of low-permeability rocks, which significantly restrict the infiltration and retention of precipitation, thereby limiting groundwater recharge.

Island aquifers are typically small, isolated, and of limited capacity, making it difficult to meet rising water demands—particularly during the summer tourist season. Intensive groundwater extraction often results in overexploitation, leading to the intrusion of seawater and subsequent salinization of aquifers, which degrades both the quantity and quality of available freshwater resources.

Moreover, the islands are situated within seismically active zones, which complicates their geological stability and water resource management further. The prevailing Mediterranean climate—with hot, dry summers and unevenly distributed rainfall throughout the year—affects the temporal dynamics of aquifer recharge. The coastal morphology, ranging from sheltered bays to steep cliffs, adds further complexity to water management practices and coastal erosion prevention strategies. The island groups in Greece are outlined in

Table 1. Classification of the Greek island groups.

Island Group	Location	Landscape and Climate	Distinctive Features
Crete	Southern Aegean	Predominantly mountainous; diverse microclimates	Southern Crete exhibits arid conditions with low rainfall and drought-prone zones.
Cyclades (e.g., Santorini, Mykonos, Naxos, Paros)	Central Aegean	Dry, rocky terrain; sparse vegetation	Islands such as Amorgos, southern Andros, Folegandros, and Anafi present arid, barren landscapes. Volcanic origin with unique geological features.
Dodecanese (e.g., Rhodes, Kos, Karpathos, Patmos)	Southeastern Aegean	Mild climate; indented coastlines with bays	Strategically located near shipping routes; popular tourist destinations. Rhodes is showing signs of desertification due to soil overexploitation, deforestation, and limited precipitation.
North Aegean Islands (e.g., Lesvos, Chios, Samos)	Eastern Aegean	Lush vegetation; abundant springs	Proximity to the Turkish coast. Lemnos features extensive sand dunes and a semi-arid landscape with minimal vegetation.
Sporades (e.g., Skiathos, Skopelos, Alonissos)	Northeastern Aegean	Dense forests; scenic beaches	Home to the Alonissos Marine Park, a protected habitat for the endangered monk seal (Monachus monachus).
Saronic Islands (e.g., Aegina, Hydra, Poros, Spetses)	Near Attica	Mild climate; easily accessible	Close to Piraeus; popular for short-term tourism and weekend travel from Athens.
Ionian Islands (Heptanese) (e.g., Corfu, Kefalonia, Zakynthos, Ithaca)	Ionian Sea	Humid climate; rich vegetation; hilly terrain	Characterized by a rugged topography, steep coastlines, gorges, and fertile valleys. The region receives the highest rainfall in Greece.

. Greek islands exhibit pronounced geomorphological diversity, characterized by limited water resources and increasing demands for sustainable water management.

Agricultural runoff and agri-food bio-waste on Greek islands contribute to significant pollution, primarily with nitrogen and phosphorus [43]. Additionally, contaminated air emissions from agricultural activities, such as ammonia (NH₃), are of concern due to their environmental and health impacts [49]. Furthermore, the management of agricultural practices and water resources in coastal areas like the Almyros basin in Thessaly, Greece, affects groundwater balance, seawater intrusion, and nitrate pollution, highlighting the importance of sustainable water management strategies [50]. Moreover, the disposal of biomass in Greece has environmental impacts, with studies focusing on anaerobic co-digestion to valorize mixtures and maximize the methane yield, particularly in Northern and Southern Greece, showcasing the potential for sustainable waste management practices in the region [51].

3.3. Water Scarcity

Water scarcity represents one of the most critical challenges faced by the Greek islands, as the limited availability of freshwater resources directly affects residents’ daily life and the functionality of key economic sectors. The main causes of water scarcity include climate change—resulting in reduced precipitation and prolonged droughts—alongside inadequate and inefficient water resource management, excessive consumption, and pollution. Moreover, increasing water demand due to urbanization and intensive tourism, particularly during the summer months, exacerbates this problem. Consequently, natural freshwater reserves are depleted at accelerating rates, leading to the salinization of aquifers and the degradation of fragile island ecosystems.

This ecological imbalance results in a marked decline in biodiversity, threatening or eliminating species that depend on freshwater environments. Simultaneously, marine pollution disrupts aquatic ecosystems and food chains, adversely impacting marine organisms and fisheries.

The socio-economic impacts of water scarcity and water pollution on the islands are significant and multifaceted. In the agricultural sector, a reduced irrigation capacity leads to crop degradation and yield losses, causing economic hardship for local farmers and increasing dependency on imported products. The intensified use of fertilizers and pesticides, combined with inefficient water use, burdens the environment further, perpetuating a vicious cycle of environmental degradation.

In the tourism sector—a cornerstone of island economies—an insufficient water supply, coastal pollution, and the deterioration of natural landscapes diminish the attractiveness of tourist destinations, resulting in decreased visitor numbers and lost investments. Local communities also face a higher cost of living due to reliance on energy-intensive solutions such as desalination, along with the public health and quality-of-life concerns associated with pollution and environmental decline.

Overall, water scarcity and pollution generate a complex web of interrelated negative impacts, necessitating immediate and integrated action across environmental, social, and economic dimensions [52].

The adoption of technological solutions, coupled with public awareness and behavioral change, can substantially mitigate these impacts. Strong political commitment and rational water resource management are essential for ensuring long-term sustainability. Key measures include protection against aquifer salinization and the development of sustainable water supply systems, such as deep groundwater extraction, dam construction, desalination, and wastewater recycling. Dams, where geographically feasible, are vital infrastructure for the drinking water supply, irrigation, and integrated water management in island regions affected by low rainfall and water scarcity. However, due to geomorphological constraints, many islands lack dam infrastructure and instead rely on desalination units.

The primary water supply solutions currently employed across the Greek islands are summarized in

Table 2. Main water supply solutions in the Greek islands.

Island	Location	Characteristics and Usage
Crete	Aposelemis Dam (Heraklion—Lasithi Regional Units)	Largest dam in Crete. Storage capacity approx. 25 million m3. Supplies water to Heraklion, Hersonissos, Agios Nikolaos, and surrounding areas.
	Potamon Dam (Rethymno)	Located on the Platys River. Used for both domestic water supply and irrigation.
	Faneromeni Dam (Heraklion)	Situated in the Mesara region. Primarily used for agricultural irrigation.
	Valsamiotis Dam (Chania)	Supports both potable water supply and irrigation.
Dodecanese	Rhodes—Gadouras Dam	Largest dam in the Dodecanese. Covers a major portion of the island’s potable water needs.
	Rhodes—Laerma Dam	Smaller in scale. Used mainly for agricultural irrigation.
	Karpathos—Schina Dam	Utilized for domestic water storage and supply.
	Kos	Lacks large dams. Employs small technical dams for rainwater harvesting and irrigation. The island depends heavily on groundwater abstraction and desalination units.
North Aegean	Samos—Karlovasi Dam	Primarily used for irrigation and partly for domestic supply.
	Ikaria—Chalaris River Dam	A small dam supporting both domestic supply and irrigation.
Ionian Islands	Corfu	Small reservoirs and minor dams used mainly for agricultural water needs.
	Zakynthos	Rainwater collectors primarily for irrigation.
Cyclades	Santorini—Vourvoulos Dam	Small-scale infrastructure with limited storage capacity.
	Syros and Naxos	Systems of reservoirs and small dams for rainwater harvesting and non-potable uses. Most Cycladic islands rely predominantly on desalination plants and cisterns.

[53]. Studies reveal that Greek islands like Mykonos, Naxos, and Kos experience significant temperature increases, potentially leading to drought episodes and water scarcity issues [54]. Additionally, the hydrogeochemical regime of islands like Samothraki showcases unique surface water characteristics influenced by geological and environmental factors, resulting in low solute concentrations and flashy stream regimes [13]. Understanding these regional variations and island-specific challenges is crucial for implementing effective water quality management strategies in Greece. The island of Crete faces similar water quality challenges to other Mediterranean islands where a significant part of its waters is brackish. Geological factors also influence water quality. The rugged, mountainous terrain and erosion-resistant rocks of Samothrace, for example, result in low solute concentrations in streams and springs. Climate change is another threat to water quality in Crete. Increased temperatures and possible droughts could affect water availability and quality [55].

Given these natural and hydrological constraints, an integrated and rational approach to water resource management is imperative. Sustainable solutions include the construction of dams and reservoirs for rainwater harvesting, the implementation of desalination technologies, and the promotion of water reuse practices. Such measures are essential to ensure water sufficiency and quality on the islands, particularly under increasing environmental stress and climate variability.

3.4. The State of Seawater Quality

The current state of seawater quality in Greek islands is influenced by the introduction of marine non-indigenous species (NISs), monitoring biases affecting the reporting of new introductions of NISs, and the need for constant and dedicated monitoring to establish Good Environmental Status (GES) [41]. Studies have identified various sources of pollution, including untreated domestic waste, marine traffic activities, plastic debris, and radioactive contamination, affecting organisms like benthic species, mussels, and pelagic fish. The presence of metals, plastics, bacteria, and radioactive elements in the marine environment poses risks to aquatic organisms, leading to toxicity, reduced water quality, and harmful algal blooms. Plastic pollution, oil spills, and factory emissions have been highlighted as major contributors to marine pollution, harming species such as sea turtles, marine mammals, and sea birds while also affecting coral reefs. Efforts to mitigate these impacts include policy interventions, public awareness campaigns, and the implementation of conservation measures to reduce plastic consumption and improve water quality [56,57,58].

In addition, pollution in Greek islands can stem from various sources like boats, tourism activities, and potential agri-food waste and industrial sources. Studies have shown that tourism, while beneficial for local economies, can pose threats to the environment due to demographic increases concentrated during peak seasons, potentially affecting coastal marine systems [59]. It is now well established that shipping emissions contribute significantly to air pollutant concentrations, with the Mediterranean Sea being a heavily trafficked area, leading to high levels of contaminants detected along the coast [56]. Furthermore, anthropogenic activities like untreated domestic waste, maritime traffic, and small-scale industrial activities, where some are close to the sea, can significantly elevate pollution levels in the study area by introducing contaminants such as nutrients, heavy metals, hydrocarbons, and microplastics, impacting the marine ecosystem and benthic organisms [60].

According to Alygizakis et al., in offshore seawaters from the Saronicos Gulf, 38 substances were detected at different depths, with amoxicillin, salicylic acid, and caffeine reaching up to 128 ng L⁻¹ [61]. Comparative studies across Greek island clusters remain scarce. Future work should focus on the contrasting hydrochemical dynamics of volcanic islands (e.g., Santorini) versus limestone-based ones (e.g., Corfu), where the geology significantly affects pollutant mobility and aquifer vulnerability.

The marine waters surrounding the Greek islands are contaminated primarily by various anthropogenic and natural sources. In particular, the following primary pollutants are described in detail.

3.4.1. Industrial and Urban Wastewaters

Industrial and urban wastewaters consist of discharged, inadequately treated effluent from industries, small-scale manufacturing units, and residential areas. These wastes commonly contain heavy metals, toxic chemicals, and organic pollutants. Pollution is frequently concentrated near urban centers and port areas. A study by HCMR (Hellenic Centre for Marine Research) in December 2022 revealed severe sediment contamination at the seabed of Syros port, with exceptionally high concentrations of chromium (~460 ppm), copper (~216 ppm), nickel, and zinc—more than double those found in comparable sites at Piraeus, Patras, and Elefsina. This pollution stems from decades of human activities, including tanning industries and ship repair yards, although the surface waters remain relatively uncontaminated [62].

3.4.2. Sewage and Municipal Wastewater

Sewage and municipal wastewater consist of untreated or partially treated sewage discharged from households and tourism facilities directly into the sea. This issue is particularly prevalent on islands with intense tourism activity and insufficient wastewater treatment infrastructure.

3.4.3. Plastics and Microplastics

Plastics constitute one of the most significant marine pollutants, with accumulated debris such as bags, caps, and other waste contaminating waters and negatively impacting marine life and the food chain. This problem is exacerbated by waste disposal at sea, either from ships or illegal coastal landfills. Microplastics—tiny plastic particles mainly derived from the degradation of larger plastic debris and from urban and industrial wastewater—pose particular concern. Studies by Suaria et al. (2016, 2018) [63,64] have highlighted the widespread presence of microplastics in the Mediterranean, with the highest concentrations found near coastal areas and ports with intense human activity. Microplastics mostly accumulate at the sea’s surface but also disperse to greater depths through marine currents and biological processes. Their presence seriously affects marine ecosystems, entering the food chain and causing toxic effects in fish and other marine species. Moreover, microplastics act as carriers of hazardous pollutants, increasing environmental risk. For example, a study by Georgia Chatziparaskeva et al. on the northern coasts of Kea found over 300 microplastic pieces per square meter, noting that the concentrations correlated more with beach orientation and wind than proximity to land pollution sources [65].

These studies underscore the need for systematic monitoring and measures to reduce microplastic pollution in the Mediterranean to protect vulnerable marine ecosystems and human health.

3.4.4. Agricultural Waste and Fertilizers

Fertilizers and pesticides reach the sea primarily through runoff. Their impact is destructive because they can cause eutrophication—excessive growth of phytoplankton that reduces oxygen levels and harms marine ecosystems. The study “Nitrogen and Phosphorus Loads in Greek Rivers: Implications for Management in Compliance with the Water Framework Directive” by Stefanidis et al. (2020) analyzed the inorganic nitrogen (N) and phosphorus (P) transport by Greek rivers into coastal waters, highlighting that rivers carry these nutrients from agricultural areas to the sea [66]. This runoff burdens coastal ecosystems, especially during periods of high agricultural activity and rainfall, causing eutrophication, which leads to hypoxic conditions and negatively affects marine biodiversity and water quality [66].

3.4.5. Petroleum Products and Chemicals from Shipping

Pollutants originate from oil leaks, fuel spills, and the use of anti-pollution chemicals by ships, particularly affecting regions with heavy maritime traffic.

The study “Investigation of petroleum hydrocarbon pollution along the coastline of South Attica, Greece, after the sinking of the Agia Zoni II oil tanker” (2021) reported concentrations of total petroleum hydrocarbons of up to 56.6 µg/L in the Saronic Gulf one year after the Agia Zoni II tanker sank [67].

3.4.6. Radioactive Pollutants and Other Specialized Substances

Radioactive pollutants are rare, usually resulting from leaks at specialized facilities or accidents. A 2019 study by Pappa et al. examined the sediments near Ierissos Bay, close to Stratoni, where a gold mine previously operated. Elevated levels of radioactive isotopes (^226Ra, ^232Th, ^40K) and toxic metals (As, Pb, Cu) were found in the surface sediments, particularly near ore loading areas, highlighting the need for monitoring and possible remediation [68]. A 2021 study by Tsabaris et al. developed an innovative marine radioactivity monitoring system using sensors integrated into a sea observation platform in the Northern Aegean, providing valuable data on spatial distribution and radiation levels to protect marine environments and public health [69].

3.4.7. The Presence of PFASs in the Mediterranean Sea

PFASs (Per- and Polyfluoroalkyl Substances) are synthetic chemicals characterized by strong carbon–fluorine bonds, giving them exceptional stability and environmental persistence. Widely used in industries and consumer products (waterproof fabrics, firefighting foams, stain-resistant coatings, and food packaging), PFASs accumulate slowly in the environment, water, and organisms, raising serious health concerns. Exposure to PFASs has been linked to hormonal disruptions, immune system damage, cancer, and other severe diseases, earning them the nickname “forever chemicals”. A 2016 study by Miroslav Brumovský et al. analyzed the distribution of PFASs in the surface and deep waters of the Western Mediterranean, finding PFASs in all samples, with the highest concentrations at the surface. River discharges and coastal areas were identified as the primary pollution sources [70]. In Greece, Zafeiraki et al. (2015) analyzed 43 drinking water samples from regions including Mykonos, Kalymnos, Syros, and Tripoli, finding 20.9% of the samples had PFASs above the quantification limits (0.6 ng/L), with the highest levels in the Aegean islands and Tripoli [71].

Beyond public health, PFASs adversely affect marine and terrestrial ecosystems by bioaccumulating in fish, mollusks, and plankton, causing reproductive, developmental, and immune system toxicity. This biomagnification increases the exposure risks for other animals and humans consuming seafood. On land, PFASs contaminate soils and groundwater, causing toxicity in plants and microorganisms, reducing biodiversity and soil fertility, and disrupting microbial communities critical for organic matter decomposition and nutrient cycling.

Greece lacks systematic and continuous PFAS monitoring programs, making population exposure levels uncertain. There is an urgent need to enhance management through integrated monitoring, stricter regulations, public awareness, and the promotion of safer industrial alternatives.

3.5. The ”Blue Flag” Program

Since 1992, the Hellenic Society for the Protection of Nature (HSPN) has served as the national operator of the “Blue Flag” program in Greece. The Blue Flag is an internationally recognized eco-label and symbol of quality, awarded under stringent criteria to organized bathing beaches, marinas, and more recently sustainable boating tourism operators (vessels) [72].

The Blue Flag is awarded exclusively to beaches and marinas that meet strict requirements across three core thematic areas:

• Bathing water quality: A beach must consistently demonstrate an “Excellent” water quality, as defined by the European Directive 2006/7/EC on the management of bathing water quality.
• Environmental management

The awarded site must implement robust environmental management practices, which include (but are not limited to)

• Effective waste management systems;
• The promotion and utilization of renewable energy sources;
• The protection and conservation of local biodiversity (flora and fauna).

3.

Services and safety

This criterion refers to the provision of high-quality visitor services, particularly for persons with disabilities, as well as

• Cleanliness and sanitation;
• Informational signage about the coastal and marine environment;
• Safety measures and trained personnel (e.g., lifeguards) to ensure the well-being of swimmers and visitors.

3.5.1. Bathing Water Quality Criteria

The quality of the bathing waters in each designated bathing area must comply with the provisions set forth in Directive 2006/7/EC of the European Parliament and of the Council on the management of bathing water quality. Sampling points are determined in areas with the maximum expected pollution load and are selected by the Special Secretariat for Water. This selection is based on various criteria, including beach visitor frequency, the proximity of potential pollution sources, and other relevant environmental factors. Water sampling is carried out by an independent, authorized, and adequately trained individual. Each sample is collected at the designated sampling location, specifically at a depth of 30 cm below the sea surface, unless the sample is related to mineral oil contamination, in which case surface water is collected. Sampling is conducted monthly throughout the official bathing season, which is defined by the Ministry of Environment and Energy (YPEN) as running from 1 June to 31 October.

In cases where the analysis results indicate a potential pollution incident or introduce uncertainty about the safety of the waters, the sampling frequency must be adjusted to allow for effective monitoring and assessment of the situation.

In the event of an oil spill, extreme weather conditions, or other exceptional events that may significantly deteriorate bathing water quality or pose health risks to bathers, the beach operator is required to temporarily withdraw the Blue Flag certification and inform the public accordingly. Bathing water quality is classified based on the criteria outlined in

Table 3. The microbiological parameters that must be monitored, along with their threshold values, to achieve an “Excellent” water quality.

Parameter	Threshold Value
Fecal Coliforms (Escherichia coli)	≤250 cfu/100 mL
Intestinal Enterococci/Fecal Streptococci	≤100 cfu/100 mL

Note: cfu = colony-forming units.

and

Table 4. The classification of bathing water quality.

Parameter	Excellent (cfu/100 mL)	Good (cfu/100 mL)	Sufficient (cfu/100 mL)	Reference Analytical Methods
Intestinal enterococci	≤100	≤200	≤185	ISO 7899-1/ISO 7899-2 *
Escherichia coli	≤250	≤500	≤500	ISO 9308-3/ISO 9308-1 *

* Retrieved from website: https://www.iso.org/ (assessed on 10 June 2025).

, as specified in Annex I of Joint Ministerial Decision No. 8600/416/E103, dated 26 February 2009.

Bathing water quality can also be adversely affected by physical and chemical contaminants, such as mineral oils and floating materials. The presence of a visible surface film or odor is unacceptable. Regular inspections of the beach must be conducted to identify such pollution. Emergency response plans must address the containment and mitigation of oil pollution and similar contaminants. The presence of floating debris (e.g., tar residues, wood, plastic, glass containers, rubber, etc.) is strictly prohibited.

As of 2025, Greece has secured the second position globally within the Blue Flag program, with 657 awards granted to beaches, marinas, and tourist boats. The regional unit of Halkidiki received the highest number of distinctions among prefectures, while the region of Crete maintained the lead at the regional level. According to the Hellenic Ministry of Environment and Energy (ΥΠΕΝ), during the 2022 bathing season, the quality of bathing waters was evaluated following statistical processing of microbiological data, which included data from the three preceding bathing seasons (2019–2021), in compliance with the criteria set forth in Directive 2006/7/EC. The evaluation results are summarized in

Table 5. The results of the evaluation.

Number of Sites Evaluated	Category	Water Quality	Percentage of Total Sites
1624	1	Excellent	98.7%
17	2	Good	1.0%
4	3	Sufficient	0.3%
0	4	Poor	0%

.

In

Table 6. Microbiological quality and pollution data for beaches in the Northern Aegean region (August 2024).

Beach	Intestinal Enterococci (cfu/100 mL)	Escherichia coli (cfu/100 mL)	Tar Residues	Glass	Plastics	Rubber	Garbage
Faros, Ikaria	0	0	NO	NO	NO	NO	NO
Kerame, Ikaria	0	0	NO	NO	NO	NO	NO
Prioni, Ikaria	0	0	NO	NO	NO	NO	NO
Fleves, Ikaria	0	0	NO	NO	NO	NO	NO
Skepsi, Ikaria	0	0	NO	NO	NO	NO	NO
Kotsampi, Ikaria	0	0	NO	NO	NO	NO	NO
Tsoukala, Ikaria	0	0	NO	NO	NO	NO	NO
Xylosyrtis, Ikaria	0	0	NO	NO	NO	NO	NO
Therma, Ikaria	0	0	NO	NO	NO	NO	NO
Kampos, Ikaria	0	0	NO	NO	NO	NO	NO
Mesakti, Ikaria	0	0	NO	NO	NO	NO	NO
Livadi, Ikaria	0	0	NO	NO	NO	NO	NO
Armenistis, Ikaria	0	4	NO	NO	NO	NO	NO
Nas, Ikaria	0	0	NO	NO	NO	NO	NO
Potami, Samos	0	0	NO	NO	NO	NO	NO
Karlovasi, Samos	0	0	NO	NO	NO	NO	NO
Kouroundere, Ampelos, Samos	0	0	NO	NO	NO	NO	NO
Kambos Beach, Vourliotes, Samos	1	4	NO	NO	NO	NO	NO
Tsambou, Samos	1	4	NO	NO	NO	NO	NO
Alykakia, Samos	2	8	NO	NO	NO	NO	NO
Tsamadou, Samos	0	0	NO	NO	NO	NO	NO
Lemonakia, Samos	0	0	NO	NO	NO	NO	NO
Kokkari, Samos	0	0	NO	NO	NO	NO	NO
Agia Paraskevi, Samos	0	0	NO	NO	NO	NO	NO
Malagari—Maounes, Samos	0	0	NO	NO	NO	NO	NO
Poseidon (Mikra Lemonakia), Samos	0	0	NO	NO	NO	NO	NO
Gagkou Beach, Samos	0	0	NO	NO	NO	NO	NO
Kerveli, Samos	0	0	NO	NO	NO	NO	NO
Poseidoniou Beach, Samos	0	0	NO	NO	NO	NO	NO
Psili Ammos, Samos	3	12	NO	NO	NO	NO	NO
Mesokampos, Samos	0	0	NO	NO	NO	NO	NO
Glykoriza, Samos	0	0	NO	NO	NO	NO	NO
Potokaki, Samos	0	0	NO	NO	NO	NO	NO
Heraion, Samos	0	0	NO	NO	NO	NO	NO
Balos, Samos	0	0	NO	NO	NO	NO	NO
Ormos Marathokampou, Samos	0	0	NO	NO	NO	NO	NO
Kampos Beach, Samos	0	0	NO	NO	NO	NO	NO
Psili Ammos (Marathokampou), Samos	0	0	NO	NO	NO	NO	NO
Limnionas Beach, Samos	0	0	NO	NO	NO	NO	NO
Seitani Mikró, Samos	0	0	NO	NO	NO	NO	NO
Seitani Megálo, Samos	0	0	NO	NO	NO	NO	NO
Agia Paraskevi, Chios	0	0	NO	YES #	YES ##	YES #	YES ##
Pantelaki Beach, Chios	0	0	NO	NO	NO	NO	NO
Velonas, Chios	0	0	NO	NO	NO	NO	YES ##
Ormos Lo, Chios	0	0	NO	NO	NO	NO	NO
Daskalopetra, Chios	0	0	NO	NO	NO	NO	YES ##
Glaroi, Chios	0	0	NO	NO	NO	NO	NO
Pantoukios, Chios	0	0	NO	NO	NO	NO	YES #
Agios Isidoros, Chios	0	0	NO	NO	NO	NO	NO
Lagkada, Chios	0	0	NO	NO	NO	NO	NO
Fanaraki, Chios	2	8	NO	NO	NO	NO	YES ##
Nagos, Chios	0	0	NO	NO	NO	NO	NO
Giosonas, Chios	0	0	NO	YES #	YES ##	YES ##	YES ###
Amades, Chios	5	20	YES ##	YES ##	YES ###	YES ##	YES ###
Agiasmata, Chios	0	0	YES #	YES ##	YES ###	YES ##	YES ###
Zanakounta, Chios	0	0	NO	NO	NO	NO	YES #
Limnos, Chios	0	0	NO	NO	NO	NO	YES #
Gonia, Chios	0	0	NO	NO	NO	NO	YES ##
Metochi, Chios	0	0	NO	YES ##	YES ###	YES ##	YES ###
Lithi, Chios	0	0	NO	NO	NO	NO	NO
Limenas, Chios	0	0	YES #	YES ##	YES ###	YES ##	YES ###
Mavra Volia, Chios	0	0	NO	NO	NO	NO	NO
Emporeios, Chios	0	0	NO	YES ##	YES ##	YES ##	YES ###
Komi, Chios	0	0	NO	NO	NO	NO	YES ##
Lilikas, Chios	0	0	NO	NO	NO	NO	NO
Gridia, Chios	0	0	NO	YES #	YES ##	YES #	YES ##
Vokaria, Chios	1	4	YES #	YES ##	YES ##	YES ##	YES ###
Limanti, Chios	0	0	NO	NO	YES #	NO	YES ##
Koukoulas, Chios	0	0	NO	NO	YES #	NO	YES ##
Agios Aimilianos (Kallimasia), Chios	0	0	NO	NO	NO	NO	NO
Agia Fotini, Chios	0	0	NO	NO	NO	NO	NO
Megas Limnionas, Chios	1	4	NO	NO	NO	NO	YES ##
Karfas, Chios	0	0	NO	NO	YES #	YES #	YES ##
Kontari, Chios	0	0	YES #	YES ##	YES ##	YES ##	YES ##
Municipal Beach of Chios	0	0	NO	YES ##	YES ##	YES ##	YES ##
Avlonas, Lemnos	0	2	NO	NO	YES #	NO	YES #
Agios Ioannis, Lemnos	28	0	NO	NO	YES #	NO	YES #
Kotsinas, Lemnos	0	0	NO	NO	YES #	NO	YES #
Saravari, Lemnos	0	0	NO	NO	YES #	NO	YES #
Keros, Lemnos	2	0	NO	NO	YES #	NO	YES #
Chavouli, Lemnos	0	2	NO	NO	YES #	NO	YES #
Mikro Fanari, Lemnos	0	2	NO	NO	YES #	NO	YES #
Fanaraki, Lemnos	0	0	NO	NO	YES #	NO	YES #
Zematas, Lemnos	0	4	NO	NO	YES #	NO	YES #
Thanos, Lemnos	10	0	NO	NO	YES #	NO	YES #
Platy, Lemnos	0	0	NO	NO	YES #	NO	YES #
Nea Madytos, Lemnos	2	0	NO	NO	YES #	NO	YES #
Richa Nera—Romeikos Gialos 2, Lemnos	1	0	NO	NO	YES #	NO	YES #
Richa Nera—Romeikos Gialos 1, Lemnos	0	0	NO	NO	YES #	NO	YES #
Skala Kallonis 1, Lesvos	0	1	NO	NO	NO	NO	NO
Skala Kallonis 2, Lesvos	1	1	NO	NO	NO	NO	NO
Mentousi, Lesvos	0	0	NO	NO	NO	NO	NO
Vathi Kritiri, Lesvos	0	0	NO	NO	NO	NO	NO
Tavari, Lesvos	0	0	NO	NO	NO	NO	NO
Skala Eresou, Lesvos	0	0	NO	NO	NO	NO	NO
Sigri Beach, Lesvos	0	2	NO	NO	NO	NO	NO
Gavathas, Lesvos	5	4	NO	NO	NO	NO	NO
Kalo Limani, Lesvos	0	12	NO	NO	NO	NO	NO
Tsichranta, Lesvos	0	0	NO	NO	NO	NO	NO
Ampelia, Lesvos	0	4	NO	NO	NO	NO	NO
Anaxos, Lesvos	3	0	NO	NO	NO	NO	NO
Petra, Lesvos	0	0	NO	NO	NO	NO	NO
Molyvos, Lesvos	0	3	NO	NO	NO	NO	NO
Eftalou (Agioi Anargyroi), Lesvos	13	4	NO	NO	NO	NO	NO
Kaya, Lesvos	0	0	NO	NO	NO	NO	NO
Tsonia, Lesvos	0	2	NO	NO	NO	NO	NO
Aspropotamos, Lesvos	0	0	NO	NO	NO	NO	NO
Xampelia, Lesvos	0	0	NO	NO	NO	NO	NO
Votsalakia (Skala Neon Kydonion), Lesvos	0	0	NO	NO	NO	NO	NO
Skala Mystegna, Lesvos	0	0	NO	NO	NO	NO	NO
Petalidi Beach, Lesvos	0	0	NO	NO	NO	NO	NO
Agios Georgios, Lesvos	7	0	NO	NO	NO	NO	NO
Kanoni (Thermi), Lesvos	7	0	NO	NO	NO	NO	NO
Skala Polichnitos, Lesvos	1	0	NO	NO	NO	NO	NO
Nyfida 2, Lesvos	6	0	NO	NO	NO	NO	NO
Nyfida 1, Lesvos	1	0	NO	NO	NO	NO	NO
Vatera, Lesvos	5	0	NO	NO	NO	NO	NO
Melinta, Lesvos	0	0	NO	NO	NO	NO	NO
Ammoudeli, Lesvos	0	0	NO	NO	NO	NO	NO
Tarsanas (Agia Paraskevi), Lesvos	2	0	NO	NO	NO	NO	NO
Plakakia (Kokkina Marmara), Lesvos	0	0	NO	NO	NO	NO	NO
Agios Isidoros, Lesvos	0	0	NO	NO	NO	NO	NO
Tarti, Lesvos	0	0	NO	NO	NO	NO	NO
Tsilia, Lesvos	0	0	NO	NO	NO	NO	NO
Ntampakariou Sourlaga, Lesvos	6	0	NO	NO	NO	NO	NO
Chalatses, Lesvos	3	0	NO	NO	NO	NO	NO
Apidias Lakkos, Lesvos	2	0	NO	NO	NO	NO	NO
Evreiaki, Lesvos	0	2	NO	NO	NO	NO	NO
Kalamari, Lesvos	0	0	NO	NO	NO	NO	NO
Tsamakia, Lesvos	0	2	NO	NO	NO	NO	NO
Xenia—Vigla 1, Lesvos	0	2	NO	NO	NO	NO	NO
Xenia—Vigla 2, Lesvos	1	0	NO	NO	NO	NO	NO
Neapoli, Lesvos	1	0	NO	NO	NO	NO	NO
Mytilene Airport, Lesvos	0	2	NO	NO	NO	NO	NO
Kratigos, Lesvos	1	0	NO	NO	NO	NO	NO
Charamida Beach, Lesvos	0	0	NO	NO	NO	NO	NO
Agios Ermogenis, Lesvos	1	0	NO	NO	NO	NO	NO
Therma, Lesvos	0	0	NO	NO	NO	NO	NO

# Small Quantity. ## Moderate Quantity. ### Large Quantity.

, indicative results from beaches within the Regional Unit of the North Aegean for August 2024 are summarized. All microbiological analyses remained within the legal limits. However, the presence of waste and plastics was observed on some beaches on the islands of Lemnos and Chios [73]. Microbiological data and qualitative observation data (on tar residue, glass, plastics, rubber, litter) were collected and evaluated for each site.

3.5.2. The Case of Crete

The quality of coastal bathing waters in Crete is systematically monitored to safeguard public health and ensure the protection of the marine environment. The Water Directorate of the Decentralized Administration of Crete is responsible for monitoring bathing waters, in accordance with Directive 2006/7/EC of the European Union.

In 2024, a total of 177 beaches across the island participated in the Blue Flag program, spanning nearly the entire coastline of Crete. Analytical results indicated that 100% of the bathing waters were of excellent quality.

From the second half of May to the first half of October, water samples were collected monthly by an accredited analytical laboratory. The parameters under surveillance included intestinal enterococci and Escherichia coli (E. coli) of fecal origin. Additionally, beaches were inspected for the presence of visually detectable physicochemical pollutants, such as plastics, tar, glass, rubber, and general litter [74].

The analytical results were outstanding: all samples from all sampling locations were within the legislative limits as defined by EU Directive 2006/7/EC for bathing waters, with intestinal rnterococci < 100 cfu/100 mL, as shown in Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8.

E. coli < 250 cfu/100 mL, as shown in Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14.

The consistently low counts of E. coli and intestinal enterococci recorded across all months (Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14) indicate the excellent microbiological quality of Crete’s bathing waters throughout the 2024 season [72,74]. These results align with previous monitoring campaigns in Crete and the wider Mediterranean, where low fecal indicator bacteria concentrations are often reported at open coastal sites, with efficient wastewater management and minimal upstream contamination sources. Seasonal stability, with no discernible increase during peak tourist months (July–August), suggests that the current wastewater treatment and coastal management measures are effective in preventing contamination, even under high visitor pressure. Maintaining such standards will be essential to sustaining the island’s tourism-dependent economy and safeguarding public health.

Furthermore, visually observable physicochemical parameters were recorded at only one beach during the entire bathing season, representing just 0.56% of all sampling sites.

Below, the results are presented per sampling location, organized by month and by parameter.

3.6. Impacts of Water Quality

Poor water quality in the Greek islands can have detrimental effects on marine ecosystems, as highlighted by various studies. The presence of contaminants can disrupt the balance of local ecosystems, impacting marine life and biodiversity [75]. Changes in water quality due to factors like eutrophication and pollution can lead to a decline in water resources and quality, affecting the overall health of the ecosystem [41]. Furthermore, climate-change-induced variations in temperature and precipitation can exacerbate water quality issues, potentially leading to drought episodes and reduced water availability for marine organisms, further stressing the ecosystems in the region [76]. Additionally, exposure to poor water quality in the Greek islands can pose significant health risks, as historical practices and modern challenges have influenced water quality management.

Poor water quality in the Greek islands, particularly in regions like the South Aegean, can significantly impact tourism due to water scarcity issues during peak seasons, such as the heavy tourist influx in the summer [41]. The need for water transportation by ships to meet the increased demand for drinking water has become exceptionally expensive, affecting the socio-economic growth of the islands [77]. Additionally, overtourism can lead to water quality degradation, as seen in a study in the Black Forest, where human pathogenic bacteria were found in touristically frequented areas, impacting the natural headwater catchment negatively [78]. The tourism industry, along with agriculture, faces challenges in adapting to water shortages, with different industries having varying levels of awareness, responsibility, and mitigation measures to address the issue [79]. These impacts highlight the interconnectedness of water quality, tourism, and industry practices in the Greek islands.

Despite identifying multiple pollution sources, few studies have quantitatively assessed their relative contributions to total pollutant loads. Future efforts should prioritize modeling pollutant fluxes from tourism, maritime traffic, and agriculture using catchment-based or source apportionment models. Finally, there is a lack of epidemiological data correlating waterborne contaminants with the disease incidence in the Greek islands. Establishing links between water quality degradation and public health outcomes (e.g., gastrointestinal illnesses during tourist season) would strengthen risk assessments.

This thematic synthesis (

Table 7. Thematic analysis of included studies.

Theme	Description	Key Findings from Included Studies
1. Sources and Types of Contaminants	Covers the origin, nature, and prevalence of pollutants in Greek island seawaters, including agricultural runoff, untreated wastewater, shipping emissions, plastics/microplastics, emerging contaminants (e.g., pharmaceuticals, PFASs), and heavy metals.	Agricultural runoff is the most frequently reported source; microplastics and emerging pollutants are under-studied but rising in concern. Heavy metals often linked to urban/industrial activity near ports.
2. Monitoring Approaches and Technologies	Focuses on the methods used to assess water quality, including traditional physicochemical analyses, microbiological indicators, water quality indices (HWQI, CCME WQI), remote sensing, IoT, AI, and citizen science.	Monitoring is often fragmented; the Blue Flag program dominates recreational water quality monitoring. The recent adoption of remote sensing and the IoT is promising but not yet widespread.
3. Regional Variations and Hydrogeological Influences	Addresses spatial differences in water quality and pollution vulnerability across island groups, considering geology, hydrology, and climate.	Volcanic islands (e.g., Santorini) show different pollutant mobility patterns compared to those in limestone islands (e.g., Corfu). Water scarcity exacerbates pollution concentrations in the arid Cycladic islands.
4. Socio-Economic and Public Health Impacts	Explores the link between water quality, tourism, fisheries, and human health outcomes.	Poor water quality negatively affects tourism revenue, increases public health risks (e.g., gastrointestinal illness), and impacts fishery productivity. Few studies have quantified economic losses.
5. Management and Mitigation Strategies	Encompasses policy frameworks (EU directives, local regulations), technological interventions (desalination, wastewater recycling), nature-based solutions, and community engagement.	The integration of technology and citizen science offers opportunities for cost-effective monitoring; regulatory enforcement remains uneven across regions.

) reveals that while the research on seawater quality in the Greek islands is diverse, it is unevenly distributed across topics and locations. Thematic clustering clarifies that future studies should focus on underrepresented areas such as emerging contaminants, economic impact quantification, and cross-sector policy integration.

Greece’s approach to sustainable development, sustainable tourism, and marine water stewardship is closely aligned with the United Nations 2030 Agenda and its 17 Sustainable Development Goals (SDGs) [80]. Within SDG 6 (Clean Water and Sanitation), the national strategies prioritize compliance with the EU Water Framework Directive and the Marine Strategy Framework Directive, targeting both traditional pollutants and emerging contaminants such as pharmaceuticals, PFASs, and microplastics. Preventive measures at the source include upgrading wastewater treatment plants to incorporate advanced filtration and adsorption technologies, implementing agricultural nutrient management plans to reduce runoff, and regulating ship-generated waste through port reception facilities. SDG 14 (Life Below Water) is supported by the expansion of marine protected areas, the Blue Flag program, and enhanced monitoring of coastal water quality, while SDG 12 (Responsible Consumption and Production) promotes circular economy models, including the valorization of agri-food by-products that might otherwise contribute to aquatic pollution. Sustainable tourism initiatives, linked to SDG 13 (Climate Action), focus on capacity management in high-demand islands, eco-certification of hospitality services, and public awareness campaigns on marine litter reduction. While these actions demonstrate progress, challenges remain in integrating these efforts into a unified, long-term marine stewardship strategy that simultaneously addresses ecological resilience, socio-economic sustainability, and emerging pollutant control.

Recent advances in environmental monitoring have introduced sophisticated analytical and predictive methods for assessing seawater quality, complementing the traditional physicochemical and microbiological approaches. Remote sensing technologies, using satellite and aerial imagery, allow for large-scale spatial monitoring of parameters such as chlorophyll-a concentrations, turbidity, and surface temperature, which are useful indicators of eutrophication, algal blooms, and pollution plumes. In Greece, Earth observation data from Sentinel-2 and Landsat satellites have been successfully combined with in situ measurements to map coastal water quality and detect seasonal changes in trophic status [81].

Fuzzy logic systems offer a flexible, rule-based approach to water quality classification, integrating multiple parameters into a water quality index (WQI) while accommodating uncertainty and imprecision in measurements. This approach has been applied in Mediterranean coastal waters to evaluating complex datasets where threshold-based classifications may be inadequate [82].

Artificial Neural Networks (ANNs) provide a powerful predictive framework for modeling water quality dynamics, especially in cases with nonlinear relationships between environmental drivers and observed conditions. ANNs have been used in Mediterranean contexts to forecast parameters such as dissolved oxygen, nutrient concentrations, and bacterial contamination, offering potential for early-warning systems in high-tourism areas [83].

The integration of these techniques in the Greek island context could address the current monitoring gaps by enabling real-time, spatially extensive, and predictive assessments, particularly important for detecting emerging contaminants, anticipating seasonal tourist pressures, and informing targeted management interventions.

4. Management and Mitigation Strategies

At the European level, water resource management is governed by a coherent and integrated legal framework, comprising key legislative instruments such as the Water Framework Directive (2000/60/EC), the Marine Strategy Framework Directive (2008/56/EC), and the Bathing Water Directive (2006/7/EC). These directives collectively promote a holistic and ecosystem-based approach to water governance, incorporating hydrological parameters, water quality considerations, and public health protection. This regulatory framework operates within the broader context of EU environmental legislation and is closely aligned with European climate change adaptation and mitigation strategies.

The current water quality monitoring programs on the Greek islands involve various innovative approaches. Τhe Ministry of Environment and Energy recorded seven short-term pollution incidents (four in Easter Macedonia and Thrace, one in South Aegean, one in Epirus, and one in Thessaly) for the 2023 swimming season during the scheduled samplings in the country’s monitoring network. The traditional methods are being complemented by citizen scientists to reduce costs and improve the data coverage, empowering decision-making [84]. Additionally, the use of advanced technologies like Internet of Things (IoT)-based systems and artificial intelligence (AI) is gaining traction for real-time monitoring of water quality parameters, although further development is needed for real-time measurements of more advanced parameters [85]. Remote sensing techniques are also being explored for monitoring water quality in coastal regions, including tracking sewage plumes, algal blooms, and oil spills, providing valuable insights into environmental health and pollution levels [57]. The existing policies and practices for managing water quality in the Greek islands exhibit varying degrees of effectiveness, influenced by several factors, including technological, environmental, and socio-economic aspects. The implementation of water quality indices (WQIs) like the Hellenic Centre for Marine Research’s HWQI and the Canadian Council of Ministers of Environment Water Quality Index (CCME WQI) has shown limitations, particularly in adapting to the diverse hydroclimatic and anthropogenic conditions of Greek rivers, which suggests a need for more tailored approaches [44].

Successful initiatives and best practices in monitoring water quality encompass a range of innovative technologies and community-driven efforts. One notable initiative is the use of remote sensors and IoT platforms for real-time monitoring, which has been effectively implemented in Tanzania’s Pangani river basin to measure parameters like pH, turbidity, temperature, and dissolved oxygen, providing accurate and secure data transmission and storage [86]. Similarly, a smart water quality monitoring system for hydroponics using the IoT and sensors has demonstrated stability and continuous data collection, highlighting the potential for automation in water quality management [87]. Citizen science projects, such as the one in the Netherlands, have also proven valuable by involving volunteers in biological water quality assessments, thus covering understudied water bodies and complementing professional data [88]. The integration of AI models with satellite imagery, as seen in the Hudson River study, has shown high effectiveness in estimating water quality indices, offering a cost-effective and rapid assessment method [89]. The use of wireless sensor networks (WSNs) has been identified as a sustainable alternative to traditional methods, enabling real-time, remote, and sensitive measurements of multiple water quality parameters with minimal human involvement [90]. Collaborative web platforms, like the one developed under the SIMILE project, enhance data sharing and stakeholder participation, crucial for coordinated water resource management in cross-border regions [91]. Additionally, the deployment of remote sensing devices on boats within a citizen science framework has been successful in the South Thyrrenian Sea, providing real-time georeferenced data [85]. Lastly, advancements in robotic systems for sewer monitoring and the use of the IoT in recirculating aquaculture systems (RASs) further illustrate the diverse and innovative approaches being adopted to ensure water quality [92]. These initiatives collectively highlight the importance of technology, community involvement, and collaborative efforts in effective water quality monitoring.

Addressing water quality challenges requires a multifaceted approach that integrates advanced technologies, nature-based solutions, and policy frameworks. One promising technological solution is the use of spatiotemporal prediction frameworks based on graph attention networks (GANs) to handle missing data and improve water quality predictions, which can be crucial for proactive management [93]. Nature-based solutions, such as floating wetlands and constructed wetlands, have shown potential to reduce urban water pollution and generate co-benefits, although their long-term effectiveness needs further documentation and assessment [94]. In high-stress regions like Egypt, riverbank filtration systems have demonstrated significant potential to improve water quality, with design considerations for the gravel-pack and pipe filter geometry being critical to optimizing their performance [95]. Deep learning models, such as CNN-BiLSTM-Attention, have also proven effective in reconstructing historical water quality data, thereby enhancing monitoring capabilities [96]. The development of nanomaterials, including magnetic nanosorbents and nanocomposites for photocatalysis, offers innovative solutions for water purification, although their environmental impact must be carefully assessed [97]. LED illumination to stimulate algal photosynthesis has shown promise in improving dissolved oxygen levels and overall water quality in freshwater ponds [98]. Policy instruments like Water Quality Trading Markets (WQTMs) can facilitate cost-effective nitrogen reduction by integrating agricultural and mussel farmers, thereby addressing diffuse nitrogen losses from agriculture [98]. Remote sensing technologies provide a valuable tool for monitoring water quality over large geographic areas, particularly for issues like algal blooms and acid mine drainage [99]. Historical insights reveal that improvements in water filtration and disinfection have significantly enhanced public health, and modern challenges such as emerging contaminants and climate variability require adaptive management strategies [100]. Finally, the collection and treatment of rainwater using conventional methods and natural mechanisms can improve water quality further for human consumption [101]. Combining these diverse approaches could create a robust framework for addressing water quality challenges globally.

Moreover, several bioactive compounds found in the low-value biomass of agri-food bio-waste, like that produced from local wineries, breweries, and olive mills, are water contaminants, as they can be transferred to water resources if not appropriately managed, while if treated as waste in waste management facilities, they not only upscale the environmental footprint but also increase the waste management costs for these local industries and communities. For example, several polyphenolic compounds and oil by-products from such agri-food bio-waste are not only emerging contaminants of surface and seawater quality but also pose a serious threat to the flora and fauna of the local aquatic environments of the Greek islands, especially their microflora, as they possess strong antimicrobial properties. From another point of view, such natural bioactives from these agri-food bio-wastes and by-products can alternatively be valorized as bio-functional ingredients in several added value applications, such as in functional foods, cosmetics, and pharmaceutical products with health-promoting properties [102,103,104]. This will not only reduce the presence of these water contaminants in the local aquatic environment but can also further support sustainable development in a circular economy design for these local agri-food industries, which is also mandated by UN and EU legislations.

Beyond technical approaches, institutional challenges, such as fragmented jurisdiction between municipalities and the lack of an enforcement capacity on remote islands, hamper consistent water quality monitoring and response efforts. Coordination between regional water authorities and tourism regulators is urgently needed.

5. Limitations—Future Perspectives

Scarce bibliographic data exist on the monitoring of contaminants in the seawater of the Greek islands, and further research is needed in order to reach a comprehensive outcome. While focusing on a specific discipline is necessary, overlooking the insights from fields such as ecology, hydrology, and social sciences could limit our understanding of the complex factors influencing water quality in the Greek islands. Similarly, while discussing management strategies is crucial, further research will enhance the insights into the practical challenges of implementing these strategies in the complex socio-economic and political context of the Greek islands.

Maintaining good water quality is crucial to the environmental and economic sustainability of islands. The increasing demand for water and the challenges of water scarcity underscore the importance of sustainable water supply methods, which must be evaluated for their environmental and social impacts [105]. Additionally, maintaining water quality is vital for preserving aquatic ecosystems, as evidenced by the relationship between water pollutants and phytoplankton diversity in coastal waters [106]. Historical and current challenges in water quality management, including emerging contaminants and climatic variability, further emphasize the need for robust strategies to protect water resources, ensuring the survival and economic viability of island communities [41]. High water quality supports the ecological balance by ensuring the health of aquatic ecosystems, such as seagrass beds and coral reefs, which are vital for biodiversity and fishery productivity [107,108]. For instance, a low rate of sedimentation and better-quality runoff water have been linked to increased seagrass net primary productivity and high fish productivity, which are essential for the livelihoods of island communities [109]. Moreover, clean water is indispensable for tourism and a significant economic driver for many islands. Poor water quality can degrade the natural beauty and health of marine environments, thereby reducing their attractiveness to tourists and negatively impacting tourism revenue [110]. Therefore, maintaining good water quality is not only vital for preserving the natural environment but also for sustaining the economic activities that depend on it, ensuring the overall well-being of island communities.

The absence of a sociocultural analysis limits our understanding of the local practices affecting water quality, such as tourism-related seasonal behaviors, agricultural habits, and citizen resistance to new waste policies. Integrating social science methods could help tailor the communication and intervention strategies.

6. Conclusions

This review highlights the dual reality of the seawater quality in the Greek islands: while many coastal bathing areas consistently achieve “Excellent” microbiological standards, serious threats from agricultural runoff, untreated wastewater, maritime emissions, microplastics, and under-researched emerging contaminants such as pharmaceuticals and PFASs persist. Monitoring remains uneven across regions, with limited adoption of advanced tools such as remote sensing, fuzzy logic, and AI-based predictive modelling.

Within the framework of the UN Sustainable Development Goals—particularly SDG 6 (Clean Water and Sanitation), SDG 12 (Responsible Consumption and Production), SDG 13 (Climate Action), and SDG 14 (Life Below Water)—Greece has taken significant steps in marine stewardship through EU directives, the Blue Flag program, and regional water quality initiatives. However, further progress is needed to integrate sustainable tourism management, pollution prevention at the source, and continuous long-term monitoring into a unified national strategy.

Future priorities should include

• An expanded monitoring scope—covering emerging pollutants, nutrient fluxes, and climate-related stressors;
• Technological integration—using IoT sensors, ANN models, and remote sensing for real-time, high-resolution water quality assessments;
• Source control measures—including targeted interventions in agriculture, wastewater management, and maritime operations;
• Socio-economic linkages—quantifying the costs of degraded water quality to tourism, fisheries, and public health;
• Community engagement—involving local stakeholders and citizen scientists in monitoring and stewardship activities.

By combining technological innovation, preventive policies, and public participation, Greece can strengthen its capacity to protect marine ecosystems, sustain its tourism economy, and meet its SDG commitments in the face of climate change and increasing anthropogenic pressures.