Challenges of Sustainable Water Management in a Heavily Industrialized Urban Basin, Case of Bytomka River, Poland

Abstract

Industrial and urban activity has inevitably changed the water environment and caused significant impacts on water resources’ quality and quantity. The identification of related impacts is particularly important in the context of increasing water shortages due to climate change. Overlapping industrial impacts and drought occurrence have resulted in the long-lasting deterioration of surface water status. Therefore, the mitigation of negative impacts is crucial for relevant and sustainable water management in river basins. One of the most impactful branches of industry is underground coal mining, which requires dewatering deposits and excavations. Mine waters discharged into rivers have induced significant increases of salinity, while urban wastewaters have increased biogenic contamination in surface waters. Sustainable development goals require water protection, energy transition, and circularity; therefore, coal will be repurposed in favor of alternative sources of energy. The phasing out of coal and cessation of dewatering of mines would rapidly reduce mine waters’ impact on the environment. However, in heavily industrialized urban basins, the share of natural waters in river flows is exceptionally low—due to significant and long-lasting transformations, industrial and urban wastewaters are the main constitutive components in certain river hydrological regimes. The case study of Bytomka in the Upper Silesian Coal Basin, Southern Poland is a vivid example of a river basin significantly impacted by urban and industrial activity over a long-term period. The Bytomka River’s water status and the development of its watershed area is an example of complex and overlapping impacts, wherein sustainable water management requires proper recognition of prevailing factors such as mine water discharges, climate change and drought periods, wastewater impacts, and urbanization of the water basin area. The presented study reveals key findings showing that future coal mine closures would result in significant water resource shortages due to a reduction of mine water discharges, significant biogenic (N and P) pollution increases, and hazards of harmful algal blooms. Therefore, there is an urgent need to increase the retention potential of the watershed, use nature-based solutions, and mitigate negative impacts of the coal mining transition. The increase in treatment capability of industrial wastewater and sewage discharge would help to cope with the natural water vulnerability induced by the impacts of climate change.

1. Introduction

Water resource scarcity is a critical issue across Europe and worldwide. It is undoubtedly exacerbated by the documented impacts related to climate change and ensuing extreme droughts. Water scarcity assessments have revealed that pollution and climate change may become more severe—doubling in 2010 and even tripling in 2050 in a clean water scarcity assessment that only considered water availability from the quantity perspective [1]. Human impacts on the water environment have had an adverse effect in areas transformed by urbanization and industry over an exceedingly long period, where the quasi-natural status of water is impossible to be restored. Most rivers are no longer free to course across the landscape unobstructed by infrastructure [2], and most major rivers no longer exhibit their historic range of flow variability [3,4]. Urban land use includes more land occupied by impervious areas such as roads and buildings. As a result, groundwater infiltration has been drastically reduced and the area available for groundwater recharge is getting smaller and smaller. Thus, groundwater depletion is one of the main problems of urbanization [5]. Unrestricted urbanization can result in a significant increase in the flow regime following the increase in the percentage of impervious cover in these catchments. The combined effect of an increase in peak flows and catchment sealing factor is to significantly increase the contribution of flood flows to annual sediment and phosphorus loads in urbanizing catchments [6].

The extent of the impact of catchment development on the quality of surface waters depends not only on the degree of development but also on the geographical location and climatic conditions, which has been confirmed by numerous regional studies. This is particularly visible in monsoon countries [7,8,9]. However, due to climate change, the impact of urbanization is also changing in European countries with relatively similar mechanisms to those in monsoon countries; moreover, the negative impact on water quality and hydromorphological conditions is multiplied due to high industrial and urban factors [10,11].

However, flow variability over time and space is a fundamental characteristic of natural rivers, and a river’s “flow regime”, in concert with sediment inputs, determines not only geomorphic adjustments but biotic composition and rates of key ecosystem processes, such as primary production [12]. Urban areas that discharge wastewater into rivers cause metals and organic substances to build up artificially, which leads to eutrophication and bioaccumulation in the ecosystem’s food chain [13,14,15]. Wastewater treatment plants in densely urbanized areas are capable of removing basic compounds (COD, BOD₅, N, and P) with conventional sewage sludge technology, while the rapid development of modern industry makes the efficient treatment of organic wastewater a critical issue. Therefore, innovative and highly effective technology solutions, i.e., carbon nanotubes [16], which aim at preventing eutrophication, heavy metals reduction, and the removal of harmful substances from wastewater are crucial for the mitigation of negative impacts on water ecosystems. Furthermore, the combined impact of urbanization and climate change has significant implications for the hydrologic cycle of watersheds. The increased presence of impermeable surfaces and the resulting structural changes in waterways, including canalization and rectification, may cause waterscapes to encounter either a shortage of water or instances of excessive runoff [17]. However, the mitigation of negative impacts on surface water is required due to relevant legal [18], socio-economic [19], and environmental aspects of water resources protection. In highly impacted water environments, sustainable management is a key challenge that should be supported by solid monitoring datasets with representative quality and quantity parameters, as well as based on the recognition of the water basin development area with a determination of prevailing impactful factors. Proposed research methods for the complex recognition of heavily impacted water basins are complementary and based on an integrated approach, considering the following factors:

• Water quality measurements from representative monitoring points;
• Flow measurement results as part of quantitative water resources assessment;
• Meteorological data (precipitation) in representative monitoring station;
• Inventory of wastewater discharges with data of quality and quantity.

Innovation in the approach of water management derives from using complex GIS datasets on the area of development connected with possible qualitative impacts on water, which are related to specific cover types and contamination. The aspects of the proper collection of monitoring datasets are of concern in a water management basis—there are limitations related to recorded length, frequency, and spatial details, which vary between data sources—as climate data are available from 1979, water body data from 1984, soil water data from 1991, river flow data from 2000, and terrestrial water storage data from 2002 onwards in many cases worldwide [20]. Proper mitigation actions in the water basin should consider results of analysis based on monitoring data, with relevant management and protection of water resources. Innovative water management in this case takes relevant and bespoke actions based on the proper recognition of prevailing impact factors. From an integrated catchment management perspective, few factors are as important in determining the quality and condition of surface water as land use, as well as limitations related to data uncertainties deriving from gaps and length of monitoring [21]. Very important as well is the recognition of direct point sources, such as discharges from wastewater treatment plants, industrial plants, and mining dewatering discharges, that can have a major impact on water quality. Often, it is diffuse pollution from anthropogenic land use changes (including agriculture, urban development, mining, and commercial forestry) that has the greatest impact on water resources.

2. Materials and Methods

The literature on water management and the potential impacts of climate change on water resources tends to fall into several broad areas. There are a number of studies of specific water management structures and systems to climate change, e.g., [22,23,24,25,26], some of which suggest potential adaptation strategies. A second group of studies explores methods for incorporating climate change into water management, both in terms of assessment techniques, e.g., [27,28,29,30]. The next group of papers examines how water managers have developed and implemented adaptation strategies in practice [31], with assessment of their implementation [32]. In fact, there have been very few studies in any sector into how organizations (here—water end users, industry actors, and wastewater treatment plant operators) are adapting to climate change. This paper contributes to the literature on case studies related to mitigation and management actions required in highly impacted water bodies facing climate change as well as the transformation of the hard coal industry.

2.1. Study Area

Bytomka River is a tributary of the Kłodnica River, located within the Odra River watershed in the Upper Silesian Coal Basin, Southern Poland. It flows through the administrative areas of three neighboring cities: Bytom, Ruda Śląska, and Zabrze, joining the Kłodnica River in the city of Gliwice. These cities are in the Silesian Agglomeration—the most industrial and urban area in Poland, with a population of about four million people living in twenty closely neighboring cities. The river receives surface runoff, industrial wastewater, and municipal sewage from the surrounding areas. Bytomka River’s springs originate at an elevation of 250–275 m above sea level. It stretches for about 19.2 km. The riverbed exhibits a significant slope, with a height difference of approximately 56.53 m between its ‘source’ and its confluence with the Kłodnica River. This corresponds to an average gradient of about 2.82 m/km. It is worth mentioning that natural springs of the Bytomka River have disappeared due to 200 years of mining drainage in the area. Nowadays the ‘source’ of the river takes the form of mine water discharge from the coal mine ‘Centrum’ in Bytom (coordinates 50°21′04.6″ N, 18°52′55.3″ E) (Figure 1).

The total catchment area is approximately 144 km² and includes one Unified Surface Water Body, designated as PLRW6000611649, classified as a carbonate upland stream with a fine-grained substrate on loess and loess-like formations. Groundwater resources within the catchment are divided into two main units. The main groundwater reservoirs are Bytom and Gliwice in the Silesian Triassic subregion. The catchment area features three aquifer levels: Quaternary, Triassic, and Carboniferous. Most of the area lies within a regional depression cone caused by over two centuries of hard coal mining, with local depressions of municipal water intakes in the northern part. The average flow rate of the Bytomka River at the water gauge station in Gliwice is approximately 2.52 m³/s, with an average annual outflow of 90.8 million m³ and a unit discharge of 0.665 million m³/km². The Bytomka River is heavily modified due to extensive mining, industrial activities, and urbanization. Most of its course is regulated and lined with stone or concrete embankments, with only a small section between Ruda Śląska and Bytom flowing through a reed-covered valley ([33], accessed on 14 March 2025).

2.2. GIS-Based Methods—Land Development

In this study, the basis for analyzing the impervious areas of the Bytomka River catchment were data collected in the Topographic Objects Database (BDOT 10 k), which is available for the entire territory of Poland. The Polish National Head Office of Geodesy and Cartography continuously update this database, and its presented status can be considered current when conducting studies at the city or regional level.

The correction of the extent of impervious areas for the years 1996 and 2010 was conducted using orthophotomaps from these years, also provided by the Office of Geodesy and Cartography. These changes involved both the removal of selected areas compared to the status and the addition of objects that have been removed in the interim period, although such cases were significantly fewer. The extent of impervious areas from the first period of industrialization was determined based on data from 1883, using a historical topographic map from that period. Due to the age of the data, there are no alternative sources that correspond more closely to contemporary data formats. The topographic map “Specialkarte der Oberschlesischen Bergeviere unter Angabe der Lage der verliehenen Bergwerke” from 1883, at a scale of 1:10,000 (Sucha Góra coordinate system), is one of the most important cartographic works of Upper Silesia from the late 19th century. This map was developed by German surveying and cartographic services specializing in documentation of mining areas. It contained detailed information on the location of granted mining claims and facilities related to the extractive industry, such as shafts, spoil heaps, and railway infrastructure. Due to its high precision and accuracy, the map served as a vital tool for mining administration and spatial planning in the region. It enables the reconstruction of the spatial layout and industrial infrastructure of Upper Silesia in the late 19th century. Its level of detail and accuracy make it a unique document of the region’s industrialization era. The territorial scope covers the entire catchment area of the Bytomka River. Development of the Bytomka River basin in relation to each analyzed state is presented in Figure 2.

The assessment of the degree of sealing and development of the catchment area was performed based on the supervised raster classification of historical topographic maps. Based on the data for the current state, made available in the vector version, developed for the needs of building a database of topographic objects, the correction of the boundaries of individual polygons defining the form of land development was performed. Most often, this operation came down to eliminating or reducing the range of polygons described by the attribute of urbanized or industrial area. Individual cases require adding polygons with such attributes in the analysis of the historical state.

2.3. Datasets of Water Quality and Flow Monitoring

For the purpose of the study datasets on surface water quality, parameters of concern, including chlorides, sulphates, TSS, EC, biogenes (N and P), BOD, DO, heavy metals, temperature, and PEW, were collected from the database of the Polish National Inspectorate of Environmental Protection for the period 1990–2024 [34]. Data were incorporated in calculations of simplified WQI (Water Quality Index) for relevant periods (1996, 2010, and 2024) to present changes of water quality in the river and tributaries impacted by wastewater discharges. Due to uncertainties of datasets, only parameters from coherent periods of monitoring were selected for detailed calculations of WQI. It is worth mentioning that datasets on surface water quality carried out by Inspectorate are collected in a database with a frequency defined according to the Polish National Monitoring Program [34]. For the purposes of this study, it important that over the period 1991–2024, the spatial distribution, range of measured parameters, and location of monitoring points in the Bytomka River basin have changed due to different requirements on monitoring and the implementation of the Water Framework Directive [18] into Polish legislation. In 2000, the EU parliament adopted the WFD, which has strongly influenced the monitoring and management of freshwater and coastal habitats across Europe. Catchment-based monitoring and planning were implemented as well in the case study area and resulted in a reduction of the wide monitoring program, frequency of measurements, and range of analyzed parameters. Therefore, the different ranges and frequencies as well as locations of measuring points in this area have allowed for WQI calculations after statistical analysis of quality parameters for relevant periods (1996, 2010, and 2024).

Complementary analysis of water balance includes data on water flows in the Bytomka River in the relevant period—these measurements were carried out by the National Meteorological Institute in Poland (IMiGW) for the period 1990–2015 [35]. The last period, 2016–2022, of monitoring periodic measurements in the flow gauge at Gliwice were collected in study [36]. As a background of the study of climate change’s effects in the Bytomka River basin, the results of annual precipitation measurements in a representative meteorological station in Katowice-Muchowiec are presented according to the data of the National Meteorological Institute in Poland [35].

2.4. Inventory of Wastewater Discharges in Bytomka River Basin

For the purposes of this study, wastewater discharge locations were prepared based on a database of water permits of the Regional Water Management Board ([37], accessed on March 2025). Data on average daily discharge and maximum limits for concentrations of contaminants were analyzed for mine water discharges, industrial discharges, and wastewater (sewage) discharges from 22 industrial and municipal objects in the river basin. The locations of wastewater discharge points, monitoring points of quality, and the flow gauge in the water basin are presented in Figure 3, marked differently (color dots—wastewater discharges: industrial—grey, sewage—orange, mine waters—black; quality monitoring—blue).

2.5. Water Quality Index Calculation

The utilization of water quality indices (WQI) and the integration of remote sensing and Geographic Information System (GIS) tools are imperative for the surveillance of these ecosystems [38]. In this study, GIS tools are used to determine features of the Bytomka River basin (impervious areas where outflow of rainwater is significant), as well as the location of measuring and discharge points in the study area.

As WQI typically comprises four processes or components, is one of the most used tools to describe water quality. It is based on physical, chemical, and biological factors that are combined into a single value that ranges from 0 to 100 and involves 4 processes: (1) parameter selection, (2) transformation of the raw data into common scale, (3) providing weights, and (4) aggregation of subindex values [39]. There are several modifications of WQI [40] depending on the number and range parameters for calculations, but in this study WQI is simplified due to data availability for the measuring points and periods of monitoring. However, according to [41], first the water quality parameters of interest are selected. Second, the water quality data are read and for each water quality parameter the concentrations are converted to a single-value dimensionless sub-index. Third, the weighting factor for each water quality parameter is determined, and fourth, a final single value water quality index is calculated by an aggregation function using the sub-indices and weighting factors for all water quality parameters. For the purposes of the presented study, parameters of concern related to salinity, water temperature, biogenic contamination, dissolved oxygen, and total suspended solids were collected—all parameters (T [°C], BOD [mgO₂/L], TSS [mg/L], DO [mgO₂/L], and PEW [µS/cm]) represent individual index terms with different weighting factors for each parameter.

The water temperature index is particularly important for biological water status and aquatic ecosystems. Water temperature is also important for its influence on water chemistry and self-purification ability. The water temperature index varies from 0 to 1. The temperature index decreases from 1 for every degree that water temperature is greater than 20 °C.

The Biological Oxygen Demand Index (BOD) indicates a high amount of organic pollution in water, which may be an indication of contamination by sewage or other waste. The BOD index reaches a high of 30 for BOD = 0 mg/L. For BOD values > 12 mg/L, index = 0.

Total suspended solids are a measure of the mass of particles suspended in water (mostly mineral), which is also an indicator of mine water discharges and rainwater outflow from industrial and urban areas. The index of TSS reaches a high of 25 for TSS = 0 mg/L. For TSS values > 250 mg/L, ITSS = 0.

The dissolved oxygen (DO) parameter is related to the biological status of surface water for aquatic organisms; the index of DO in this study reaches 25 when dissolved oxygen > 10 mg/L; for DO values = 0 mg/L index is equal to 0.

The conductivity (PEW) of surface water is particularly important in the case of identification of saline mine water discharged into the river. The index of PEW reaches a high of 20 when the conductivity is 200 μS/cm (conductivity of drinking water). For conductivity values greater than 4000 μS/cm, the index value is equal to 0.

A simple additive aggregation function for the water quality index is expressed as follows:

$$WQI={\sum }_{i=1}^n{s}_i{w}_i$$

where s_i is the sub-index value for parameter i, w_i (ranges from 0 to 1) is the corresponding parameter weight value, and n is the total number of parameters.

The WQI suggests 5 quality classes ranging from poor (0–25), fair (26–50), average (51–70), and good (71–90) to excellent (91–100) [41].

3. Results

The Bytomka River is highly affected by industrial and urban activity. Analyses of land development and quality and quantity of water in the river basin, as well as the identification of prevailing impacts on the water environment, have revealed that sustainability and proper management actions are necessary to increase its resistance. Practical actions as well as legislative solutions are possible to be undertaken after the proper identification of impacts and their range and acuteness.

3.1. Land Use and Impervious Surface Trends

Considering land development and analysis, the percentage of impervious areas in the relevant periods changed as follows:

• 1883—5.8%;
• 1996—20.3%;
• 2010—21.1%;
• 2024—22.8%.

This means that in the last three decades, impervious areas in water basin have been rather stable, but still consist of about 32 km² in the central part of the study area. This means that rainwater outflow is discharged directly to the river corridor, with very low possibility of retention and detention. In reference to research studies, urban land use has a significant influence on stormwater quality. Metal concentrations and nitrogen compounds were particularly sensitive to variations in land use, whereas phosphorus forms and total suspended solids showed relatively consistent levels across different land use types [42]. The highest pollutant loads were observed in runoff from roads, city centers, and commercial areas, while single-family residential zones generated the cleanest runoff. Pollution levels in industrial areas were moderate, likely due to the diverse nature of industrial catchments [37].

3.2. Flow Variability and Water Quantity in Bytomka River 1990–2022

Water flows in the Bytomka River have changed in a wide range of mean annual values, which is significant in the high flow records, while mean low flows have been decreasing systematically—in the last decade, low flows have decreased twice compared to the beginning of the 90s. This has been observed in small rivers with a highly affected water regime by industry and urban discharge, where natural water flow is lower percentage in the total measured flows. High mean annual flows are then affected by changes related to intense and very high precipitation—mean values are extremely high, but this flow lasts briefly (total maximum monthly means were noted during flash floods in July and August 2010—28.3 m³/s and 13.2 m³/s, respectively). In Figure 4, the changes of the annual mean flows in the Bytomka River are presented. In Figure 5, the mean annual precipitation according to data for the Katowice–Muchowiec meteorological station are presented.

Considering the association of climate (here: precipitation) data with flow changes, it is revealed that the reduction in precipitation leads to an intensification of low flow. As it is marked in Figure 4 and Figure 5, in the last decade significant drought is observed. The very low annual mean precipitation in 2011, 2015, 2018, and 2022 and the significant flow drops in the Bytomka river are correlated. Moreover, since 2010 (flood occurrence), there have been changes in the intensity and frequency of occurrence of maximum and minimum flows compared to previous periods.

3.3. Water Quality Trends and WQI Analysis in Surface Waters of Bytomka River Basin in 1990–2024

The changes (deterioration) of surface water in the Bytomka River and the tributaries affected by wastewater discharges have been analyzed considering available data from National Monitoring [34]. The results of calculations of simplified WQI are presented in Figure 6.

Simplified WQI has been calculated for periods 1996, 2010, and 2024 due to the availability of data on parameters of concern. The changes (deterioration) of surface water are significantly visible in the last period of monitoring, which is particularly impacted by climate changes and drought with alternately occurring high flush flows due to sudden and short-lasting intense rainfalls. WQI based on the parameters of temperature [°C], BOD [mgO₂/L], DO [mgO₂/L], TSS [mg/L], and EC [µS/cm] mainly revealed deterioration of the water in the Bytomka River, especially in the last period of measurements while relatively very low flows have occurred. It is important to note that the outflow to the Kłodnica river (the last measuring point and flow gauge location) is the measurement profile where the total status of the Unified Surface Water Body designated as PLRW6000611649 is assessed according to the Water Framework Directive regulations. This assessment is representative for the status of this water body, while in general the deterioration of water quality is observed within the watershed area. Water quality data analysis of trends was performed. In Figure 7, Figure 8 and Figure 9, the trends of temperature [°C], BOD₅ [mgO₂/L], and PEW [μS/cm] are presented for the period 1990–2024 according to the available data of the National Monitoring Program [34].

The quality of water in the Bytomka River during the period of 1990–2024 has changed significantly. The prevailing impacts are generally related to salinity increases, while biogenic contamination has continuously decreased in the analyzed period.

3.4. Pollution Sources and Identification of Prevailing Impacts on Waters in River Basin in 1990–2024

Sustainable water management in highly impacted water basins requires also the identification of users of so called ‘water services’, which means, according to the WFD, i.e., wastewater discharge to surface water. In the study area, according to the Cadaster of water permits of the Reginal Water Management Board [37], Gliwice, Poland, there are 5 discharges of saline mine waters (from underground coal mines), 10 discharges of sewage (5 municipal wastewater treatment plants), and 7 industrial wastewater discharges. According to water permits issued in the last period of 2010–2024, the total average daily discharge is presented in

Table 1. Wastewater discharges in Bytomka River basin.

Discharge	Q Average [m3/day]	Characteristic Limits of Contaminations in Water Permits
Saline mine waters	81,326	Chlorides 1000–6500 [mg/L] Sulphates 500–2000 [mg/L] TSS 35 [mg/L]
Wastewater (sewage)	61,580	BOD 15–40 [mgO2/L] COD 125–150 [mgO2/L] N 10–30 [mg/L] P 1–50 [mg/L]
Industrial wastewater	2005	Cu 0.5 [mg/L] Cr 0.1–0.5 [mg/L] Pb 0.5 [mg/L] Hg 0.06 [mg/L] Ni 0.5 [mg/L]

.

Total wastewater discharge in the Bytomka River basin (to Bytomka River and its tributaries), according to water permits issued in the last decades, in daily average is 144,911 m³/day, which means that 1.67 m³/s is wastewater flow from all 22 discharge points. Compared to the annual mean flows in the measuring point in the outflow to Kłodnica, this indicates a river with a sparse tributary network that is mainly fed by mine waters, industrial discharges, municipal wastewater, and stormwater runoff. A significant share of the river’s flow (estimated at 60–90%) consists of treated and untreated wastewater. The constant discharge of saline mine waters helps to maintain a steady flow during periods of low rainfall and high temperatures. However, the overlapping impacts from the three cities limit the river’s self-purification capacity. The hydrological regime varies along the river’s course, with increased flow velocity in the lower sections, which is visible in increase in salinity of waters in Bytomka, while biogenic contamination has decreased over the analyzed period. This is particularly important in the case of environmental flows, which describe the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and wellbeing that depend on these ecosystems. In the case of Bytomka, the rough estimate of environmental flow depends on the water balance in the watershed. In this highly impacted river basin, the water balance is disturbed by the long-lasting influence related to industry, urbanization, and land development, and the water balance strongly depends on these impacts. Therefore, the environmental flow would be on average 1.1 m³/s, which is a rough estimate of the natural outflow of fresh water in the river basin. This is about 10% of the mean average low flow in the analyzed river.

3.5. Uncertainties of Analysis, Limitations, and Data Gaps Identified in the Case of the Bytomka River Basin

Considering the limitations of this research, several data gaps and uncertainties should be underlined. The data gaps are mostly related to the availability of monitoring results from the period of 1990–2024. In this period, the monitoring requirements, data collection, and legal basis have changed to fulfill several regulations related to water policy. Inconsistency in the range of parameters, as well as simplifications of the river model, in such a complex basin should be treated as estimation to make the assessment of water quality and quantity possible. Therefore, WQI was simplified and calculated to present the long-lasting impact of industrial and urban activities with relevant identification of prevailing factors, which are now mostly related to mine water and coal industry impacts. Considering the coal industry transition in the near future, it is highly important to identify appropriate measures in water management.

4. Discussion

The river basin has long been acknowledged as the appropriate unit for water resources management. The multi-functional use of water resources under varying hydrological, environmental, and socio-economic circumstances require an integrated approach to river basin management, and this is a major challenge. The concept of integrated river basin management requires a holistic approach that combines the management of environmental components and human activities with the objective of sustainable development and use of the water resources while maintaining ecosystem integrity [43]. In this case, it is very important to tie the findings back to concepts like environmental flows and integrated water management. The concept of using nature-based solutions and policy management in release water permits for several users in a holistic analytical process of water balancing is crucial for the future protection of water resources. This concept of River Basin Development Planning and Management (RBDPM) has been used for development planning and management since the 1930s. Various forms of river basin development planning and management have been applied in many countries. Unfortunately, the results have often been disappointing [44]. Traditionally, water has been managed from a supply perspective and, like in the case of the Bytomka River, from the perspective of wastewater receiver, with an emphasis on maximizing short-term economic growth from the use of water (or water services, in the terms of the WFD [18] and Polish Water Act [45]). The aim of water management according to Polish regulation is to meet the needs of the population and economy, as well as to protect the waters and the associated environment, in particular as regards (1) ensuring adequate quantity and quality of water for the population; (2) protection against flood and drought; (3) protection of water resources against pollution and improper or excessive exploitation; (4) maintaining or improving the quality of water ecosystems and those dependent on water; (5) providing water for agriculture and industry; (6) creating conditions for energy, transport and fishing; and (7) satisfying the needs related to tourism, sport, and recreation [45]. Apparently, no consideration has been given to the health of the resource itself, and there is a poor understanding of the implications of overuse or declining river health. Maintaining ecosystem integrity implies that a certain level of flow with an acceptable level of water quality is there in the system, and this is considered as environmental flow. Environmental flows are not empirically determined figures, but they are value judgements depending on what the aim of river management is [46]. In the presented case study, while almost 90% of the measured flow is discharged wastewater and mine water with relatively poor quality with rainwater outflows, the environmental flow of this river is below the 10% threshold for the possibility of maintaining the water ecosystem. It is worth mentioning that the environmental flow reaches about 10% of the annual low flows. The WQI determined for several monitoring cross sections is below the average of decades, which visualizes poor quality. Moreover, the water management practices and legislation in Poland lacks mechanisms of proper discharge management—water permits are issued without consideration of water balance, as well as without recognition of other water users in the total area of the river basin. The unsustainable use of water resources is significant in industrial and coal mining regions like USCB, where it is very difficult or even impossible to implement mitigation solutions to improve the water quality status or protect water resources to be used, i.e., for municipal use. The share of impervious areas within the river basin often results in direct outflow of rainwater without any retention. The Bytomka River, with a relatively high impact of industrial areas and urbanization on water balance, is an example of the loss of hydraulic and hydrogeological connectivity of surface and groundwaters, which results in a lack of water recharge. Long-lasting mining activity (about 200 years of underground coal and Zn-Pb ore mining with related mining drainage) have significantly depleted water resources in this area. The aspect of mine water discharges should be considered as well in terms of the coal mining transformation and the period of phasing out of coal. This means that mine water discharges in the coming decade would be decreased or even ceased (pumping water from abandoned, interconnected mines would be reduced due to the end of coal exploitation), which will result in a significant reduction of total flow in the receivers—Bytomka and its tributaries. Taking the rough estimation from Table 1, 0.94 m³/s of mine waters would no longer be a ‘source’ of flow in this river, and therefore the chemistry of the surface water in the river basin would be affected by a higher potential for eutrophication due to biogenic contamination and increased phosphorus and nitrogen contamination, which leads to harmful algal blooms (HABs). An example of multiple stressors that produced an environmental disaster in a large European river is the Oder River, where a toxic bloom of the brackish-water planktonic haptophyte Prymnesium parvum (the “golden algae”) killed approximately 1000 metric tons of fish and most mussels and snails. The massive Prymnesium HAB would not have been possible under natural conditions but was enabled by the combination of chronic and acute impacts—chronic high salt load, replete nutrient concentrations, flow velocity reduction through impoundment, and acute climatic forcing, including high air and water temperatures and low river discharge (in this understanding as environmental flow) [47]. It is worth noting that wastewater and mine water discharges are not flow-dependent in Polish legislation—while low flows and significant and long-lasting droughts occur in water basins, there are no dedicated legislation and management tools to be implemented in use of water services (wastewater discharges, water withdrawal, etc.). However, the presented study case has revealed that actions related to legislation and increasing retention should be implemented in the scale of the water basin. Therefore, the legislative aspects are mostly related to proper balance of the use of water services—wastewater discharge quantity limits should be determined in water permits with respect to disposable water flows in the river. Moreover, limits of salinity and possible buffering capacity of the river to dilute salts in natural waters are severely decreased due to drought periods and long-lasting low flows due to climate change. Sustainable discharge of saline mine waters is possible with use retention systems based on surface reservoirs with continuous controlling systems of EC in discharged mine waters. Sewage systems based on circularity and water reuse systems could also improve water body status via increasing the retention and possible use of freshwater from that alternative source. To implement this action, it is obvious that not only legislation but organizational and financial issues should be engaged, but the first step of the identification of prevailing impacts in surface waters in basin areas should be performed. In the study area, the possibility of an increase of retention potential in the water basin area with use of Blue-Green Infrastructure solutions (e.g., reuse of rainwater, especially in impervious areas) would be beneficial for water resources and their quality and quantity. Considering the methodology for estimating environmental flows in Poland, it is worth mentioning that the most important problems are related to the currently updated water management plans. Overestimating environmental flows may result in a reduction of water resources available to other water users, especially industrial and urban wastewater discharges in the river basin.

Detailed planning of water management in highly impacted water basins requires detailed economic cost calculation. The implementation budget for a revitalization plan in the Bytomka River basin may cost millions of PLN, spent directly on actions of improvement of water status as well as restoration of the watershed area. The City of Ruda Śląska has obtained nearly PLN 19.9 million in funding for a project to re-naturalize the Bytomka River Valley. The investment, worth over PLN 21 million (5 million USD) in total and financed from the European Union and the State Budget, aims to restore the natural landscape and create an attractive, green space for residents.

5. Conclusions

The long-lasting impact of industry, urbanization, and—as in the presented study—coal mining results in significant impacts on and the deterioration of surface water resources. Sustainable water management in such an impacted and completely changed water basin requires an individual approach with relevant identification of the prevailing negative impacts, possible mitigation actions, and tools for its implementation. Implementation of these mitigation actions (e.g., increasing retention potential and reuse of water, with relevant discharge management) would not restore the water environment completely—this is impossible in conditions of such impacted and deteriorated water basin. However, due to the industrial transition and climate change impacts, it is crucial to properly recognize possible changes in the water environment. The presented study reveals that the long-lasting industrial and mining impacts on the water environment are intensified by global changes due to long-lasting droughts and water shortages. The conditions determined by physical, economic, and environmental factors or processes will increase the susceptibility of the water environment to the impacts of hazards related to climate change. Therefore, the implementation of possible, scalable, and gradual solutions in water management and protection would increase the restoration potential of water basins. Moreover, due to gaps in monitoring datasets, efforts were made to confirm the interpretation of data analysis and research background. Satellite instruments as well as GISs can provide a near-immediate global overview of climate and water conditions, but they have uncertainties. Where available, onsite observations are usually more accurate and necessary to calibrate remote sensing approaches like those used here. Protecting and expanding the remaining water measurement station network should be a priority for appropriate selection and implementation of mitigation measures in river basin (i.e., quantity of retention solutions and flow-dependent discharges). The example of the Bytomka River is relevant as well for other coal regions within Europe (or even globally) where there is a significant influence of urban and industrial discharges on water quality and quantity status.