Global Evolution and Methodological Trends in River and Lake Health Research (1991–2024): A Bibliometric and Systematic Review

Abstract

River and lake health assessment has evolved from a purely ecological concept to a multidimensional framework integrating ecosystem integrity and social service functions. Based on a comprehensive dataset of 1412 papers (1991–2024), this study combines bibliometric mapping with a systematic review to track the evolution of biological monitoring and assessment methodologies. Quantitative analysis of keywords reveals that while traditional focuses on heavy metals, fish, and sediments remain dominant, there is a significant shift towards integrated frameworks where biological indicators (e.g., benthic macroinvertebrate integrity and fish retention) are increasingly coupled with social services. We critically review three assessment paradigms: single-factor bio-indicators, biological predictive models such as RIVPACS and AUSRIVAS, and multi-factor comprehensive models. The study identifies critical gaps in ecological connectivity and the management of transboundary lakes under climate change. Consequently, we propose a strategic roadmap leveraging the National Ecological Connectivity Optimization Platform and mandatory “health audits” for transboundary waters to ensure the long-term sustainability of aquatic biodiversity. This review provides a scientific basis for balancing biodiversity conservation with sustainable water resource utilization.

1. Introduction

Since the 1970s, growing concerns about environmental degradation and the unsustainable use of resources have fueled the development of river and lake health, along with related theories [1]. In 1972, the United States enacted the Clean Water Act, which is considered the earliest documented expression of river health. Since then, people have gradually begun to pay attention to the protection of river and lake water bodies [2]. In the 1980s and 1990s, countries such as the United Kingdom (1984), the United States (1989), Australia (1992) and South Africa (1997) innovatively proposed the concept of river and lake health [3]. Building on these developments, Schofield [4] defined river and lake health as the degree of similarity between these ecosystems and undisturbed systems, particularly in terms of biodiversity and ecosystem functions. Meanwhile, Fairweather [5] emphasized the integration of socio-economic objectives with ecological health.

In the process of foreign research on river and lake health, opinions differ on whether the concept should encompass social service functions. Two main perspectives have emerged: one focusing on the natural attributes of rivers and lakes, and the other on their social service functions [6,7]. The natural attribute of rivers and lakes points out that the health of rivers and lakes refers to the healthy state of their natural attributes, which mainly includes the morphological structure, material circulation and energy flow, and can resist external interference to a certain extent and maintain the structural stability of river and lake ecosystems [8]. As the concept of river and lake health has evolved, scholars have increasingly viewed it as a balance between ecosystem integrity and social service value [9]. This broader perspective is particularly important in China, where both ecological and social factors have been incorporated into official assessments. The focus has shifted from merely restoring ecological integrity to promoting a dual goal of ecological health and human well-being [10,11]. The widely accepted international definition holds that healthy rivers and lakes should not only maintain ecological functions but also provide essential services for humans, such as recreation, cultural engagement, and education. Key indicators for evaluating social benefits include recreational value, which is assessed based on accessibility, facilities, and environmental quality, as well as cultural significance, which reflects how rivers and lakes contribute to local identity. Economic value highlights the role of these water bodies in supporting local economies, particularly through tourism, agriculture, and fisheries. However, the assessment of social service functions relies not only on social benefit indicators but also on fundamental indicators such as flood prevention and water supply security. These ensure disaster risk reduction and the stable provision of water resources. Additionally, public satisfaction serves as a reflection of social effectiveness, further demonstrating the coordination between ecological health and societal needs. Overall, the health of rivers and lakes is not only an ecological issue but also deeply impacts social, cultural, and economic systems.

Compared to other countries, river and lake health research in China began relatively late and has evolved through distinct stages with increasing complexity. In 2002, Tang Tao introduced the concept of river and lake health to China, using algae, invertebrates, and fish as key indicators to assess ecosystem health. He classified evaluation methods into prediction models and multi-indicator approaches, emphasizing that healthy rivers and lakes should be a primary goal for water management [12]. Since then, domestic scholars have extensively studied the concept, evaluation methods, indicators, and models of river and lake ecosystem health. However, due to different national contexts, countries like those in Europe, the United States, and Australia do not face the same issues of water pollution and supply-demand conflicts that China does. Therefore, the concept of river and lake health in China is more unique and multifaceted compared to foreign definitions. Based on national circumstances, the Chinese government and river basin management agencies have actively advanced river and lake health research, building on both domestic and international findings. In 2004, the Yellow River Conservancy Commission of the Ministry of Water Resources proposed the goal of maintaining the health of the Yellow River. A year later, in 2005, the Changjiang Water Resources Commission of The Ministry of Water Resources introduced a new approach to river management, aiming to “maintain the health of the Yangtze River and promote harmony between people and water.” In 2010, the Ministry of Water Resources of the People’s Republic of China initiated a national pilot project for the health assessment of major rivers and lakes (Table S1). A key milestone came in 2020 with the release of the “Technical Guidelines for River and Lake Health Assessment (Trial),” which formalized comprehensive evaluation criteria, including ecosystem resilience and social service functions [13]. These guidelines, along with regional documents like Jiangxi Province’s “River and Lake Health Evaluation Guidelines” (DB36/T 1404-2021) [14], provide a systematic approach to river and lake health assessment. They formalize criteria covering ecosystem resilience, social service functions, and other crucial factors, tailored to local conditions. The assessment index system includes ecosystem structural integrity, resilience to disturbances, and sustainability of social services, offering practical tools for effective management and protection. The assessments are based on four criteria: “basin,” “water,” “biology,” and “social service functions.” For instance, the Jianghan District’s West Lake case study demonstrates how metrics such as water clarity and public satisfaction surveys help operationalize this approach [15]. This framework aids in identifying issues, analyzing root causes, and increasing public awareness, while providing river and lake managers with a solid foundation for informed decision-making and long-term management (Figure 1) [16].

In recent years, China has successively proposed distinctive and meaningful concepts of river and lake health, such as “Healthy Life of the Yellow River,” “Healthy Yangtze River,” and “Strengthening the River and Lake Chief System, Building Happy Rivers and Lakes.” As the concept of water ecological civilization continues to evolve, the integration of regional socio-economic development with the natural attributes of rivers and lakes has gained importance, with social service values gradually incorporated into river and lake health. Zhang [17] synthesized these advancements and aligned them with new challenges, proposing a comprehensive framework for river and lake health. This framework emphasizes both the integrity of ecosystems and the coordination between these ecosystems and the social services they provide. A substantial body of research has been dedicated to river and lake health, covering areas such as modeling [8,16,18], indicator selection [19,20,21], and river and lake management and conservation [22,23,24,25].

This paper analyzes research on river and lake health from the Web of Science Core Collection (1991–2024), utilizing CiteSpace and VOSviewer for literature visualization to identify research frontiers, hotspots, and trends. Using this approach, the study systematically integrates global research trends on river and lake ecosystem health for the first time, offering new perspectives and directions for academic inquiry. To enhance the practical relevance of this work, we propose several innovative policy recommendations. For example, we suggest integrating data, models, and case libraries from the National Ecological Connectivity Optimization Platform into policy implementation, fostering a closer connection between academic research and policy practice. Additionally, we advocate for mandatory health audits of transboundary lakes, aiming to ensure the long-term sustainability of these ecosystems.

2. Data Sources and Research Methods

2.1. Data Sources

To quantitatively analyze and organize research in this field, literature on river and lake health was selected from the Web of Science Core Collection databases, covering the period from1 January 1991, to 24 May 2024. The search was conducted using the formula: TS = ((River and lake health) OR (River and lake ecosystem health) AND (model) AND (evaluate) AND (indicators)). The sample was subject to strict inclusion/exclusion criteria, which involved selecting only peer-reviewed articles published in academic journals. Non-English studies were excluded to maintain consistency and comparability of data, which may introduce potential bias toward Western perspectives. However, as shown in the bibliometric analysis of authors and countries, Chinese scholars contributed a significant proportion of the publications, suggesting that the potential bias toward Western perspectives may be limited in this case.

To ensure accuracy, the retrieved papers were carefully screened, resulting in 1412 valid papers. The literature visualization analysis was performed using CiteSpace (v.7.0) and VOSviewer (v.1.6.20), which objectively reveal the research frontiers, hotspots, and development trends in river and lake health. This process follows the systematic review standards outlined in Wetland Ecological Quality Assessment (HJ 1339—2023) and the PRISMA statement, ensuring transparency, standardization, and rigor throughout the selection process, thereby enhancing the reliability of the findings. For more detailed research methods, please refer to the Supplementary Materials. Based on these findings, relevant suggestions are provided to offer a reference for scholars, helping them better understand the overall research status in this field.

2.2. Data Cleaning

The data obtained through the database may contain duplication or be inconsistent with the subject without careful screening. Therefore, the data needs to be cleaned before analysis to avoid affecting the analysis results due to quality problems of the data itself and to ensure the effectiveness of visual analysis. This article utilizes the “DEAN” data cleaning process, which is designed to mitigate the negative impact of data quality issues. The “DEAN” process addresses duplicate entries, erroneous records due to retrieval deviations, inconsistent keywords (aliases with different structures), and low-frequency or irrelevant keywords (noises). The steps and outcomes of this data-cleaning process are presented in Table S2 and Figure 2a.

2.3. Data Integrity Analysis

Statistical analysis of the literature data revealed that the 1412 papers included in this study were contributed by 6687 authors (including co-authors) from 2027 institutions across 102 countries and were published in 198 journals.

Figure 2b illustrates the changing trend in the annual number of research papers in the field of river and lake health. During the period 1991–2010, the number of publications per year fluctuated between 1 and 19. In general, the number of publications in the field at this time was minimal. During the period from 2010 to 2019, the number of publications in this field increased significantly. After 2019, the number of publications rose sharply, stabilizing at over 140 per year from 2020 to 2023. The peak was reached in 2022 with 198 publications, highlighting the growing attention and interest in this research area in recent years.

3. Descriptive Statistics

3.1. Bibliometric Analysis of the Author

By analyzing the authorship of relevant literature, we can identify key scholars and core research groups in the field of river and lake health. Goldberg [26] observed that approximately half of the publications in any scientific field are produced by a small group of highly productive authors. This pattern is consistent with Price’s Law, which formalizes the relationship by stating that the number of core authors (m) is approximately 0.749 times the square root of the number of publications by the most prolific author (n_max):

$$m=0.749\ast \sqrt{{{\displaystyle n}}_{\max }}$$

(1)

In this study, nₘₐₓ was found to be 14, based on VOSviewer statistics. Therefore, the minimum threshold for identifying core authors is m ≈ 2.80. Authors with three or more publications were considered core contributors, totaling 278 authors and accounting for 1064 publications—75.4% of the total sample—well above the 50% threshold suggested by Price’s Law. This suggests a consolidated and influential cohort of researchers in this domain.

To further examine collaboration patterns among these core authors, a co-authorship network analysis was conducted using VOSviewer. The analysis included 1412 publications authored by 6687 individuals. The network visualization (Figure 3a) maps relationships among authors with three or more publications. Each node represents an author, with size reflecting publication count and connecting lines indicating co-authorship links. A color gradient reflects the average year of publication, offering a temporal dimension to author activity. Several well-defined clusters are evident in the visualization, indicating the formation of stable research teams and international collaboration networks. Prominent figures such as Zhang Lu, Wang Jun, and Yang Zhaoguang stand out as highly productive authors who also occupy central positions within the network—demonstrating strong connectivity and frequent co-authorship. In terms of network metrics, VOSviewer represents centrality through degree centrality, where the “degree” of a node indicates how many direct connections an author has with others. A higher degree suggests greater influence and connectivity within the research community. This is reflected in the numerous co-authorship links surrounding key figures, particularly Zhang Lu and Wang Jun (Figure S1a). Network density, another critical metric, is also visualized using a heatmap in the density view (Figure S1b). Density reflects the ratio between actual and possible connections within the network. High-density areas (shown in deep red) signify regions of intense scholarly collaboration. Scholars such as Zhang Lu, Giesy John P., Wang Jun, and Yang Zhaoguang are located in the densest zones, highlighting both the productivity and collaborative influence of these authors.

Publication and citation statistics further illustrate author prominence. Zhang Lu leads with 14 publications and 444 citations between 1991 and 2024, averaging 31.7 citations per article. His research primarily focuses on ecological risks posed by pollutants, especially emerging contaminants, in aquatic systems [27,28,29]. Memet Varol and Wang Jun each have 11 publications, with average citation counts of 45.6 and 35.8, respectively. Their research addresses environmental pollution, limnology, and contaminant transport [30,31,32,33] (Figure 3b). Most of these scholars are affiliated with disciplines such as water resources engineering and environmental science. Overall, the network visualizations and bibliometric indicators highlight the rise of a core group of authors who not only make substantial contributions to the literature but also act as a unified and collaborative force. Their academic impact and strong connections play a crucial role in shaping the intellectual framework and ongoing progress of river and lake health research. The VOSviewer parameter settings are shown in Table S3.

3.2. Bibliometric Analysis of the Journal

By counting the distribution of journals where these papers are published, it is evident that over the past thirty years, except for a few comprehensive journals, the majority of publications in this field are concentrated in the areas of water resources research and environmental science. Figure 3c lists the top ten journals based on the number of published papers. Notably, two journals have more than 100 articles: Science of The Total Environment with 149 articles and Environmental Science and Pollution Research with 121 articles.

Among these journals, Water stands out as an open-access journal, highlighting the significant role that open-access publishing has played in advancing research in this field in recent years. Although there are still differences among scholars on the best way to achieve open access, the idea that research results should be provided free of charge has been widely accepted. An analysis of journal citations shows that Chemosphere, a leading journal in environmental sciences, has the highest average citations among the journals listed in Figure 3d. With 58 articles and an average of 51.98 citations per article, this indicates that the papers published in Chemosphere are of high quality and have garnered significant attention in the field.

3.3. Bibliometric Analysis of the Country

To identify the countries that have made the most significant contributions to river and lake health research, this study analyzed publication data from 102 countries. Using VOSviewer and Scimago Graphica (v.1.0.53), we visualized the countries with 10 or more publications, focusing specifically on the top 30 in terms of publication volume. The results are shown in Figure 4. In Figure 4a, larger circular nodes represent a higher number of publications and the lines connecting nodes indicate the strength of collaboration between countries—the thicker the line, the more frequent the cooperation in publishing. The distribution of publications across countries is highly uneven, with a strong top-tier effect. A majority of the papers originate from scholars in just a few countries.

To analyze international trends in river and lake health research, we divided the literature into three periods: 1991–2000, 2001–2010, and 2011–2024. The number of published literature reflects the degree of attention and research on the health of rivers and lakes in different periods. From 1991 to 2000, research on river and lake health was in its early stages, with only 32 papers published globally. During this period, only a few countries, such as the United States, Canada, France, Australia, and South Africa, conducted relevant studies (Figure 4b), with the United States and Canada leading the research efforts. The period from 2001 to 2010 was in the development stage of global river and lake health research, with a gradual increase in both research activities and publications, totaling 111 papers. During this time, developing countries like China and Brazil began contributing to the field (Figure 4c). However, the primary research efforts were still concentrated in developed regions, particularly Europe and the United States. From 2011 to 2024, with growing global awareness of the importance of river and lake health, the number of publications surged to an impressive 1269 papers. This period saw more developing countries engaging in research on river and lake ecosystems, recognizing it as a crucial strategy for preserving the health of these environments (Figure 4d).

In summary, developed countries like the United States, Canada, and Australia were early leaders in river and lake health research and have sustained strong growth. Between 2011 and 2024, developing countries such as China, South Africa, Iran, India, and Brazil made substantial contributions to the global body of research in this field. China, in particular, had the highest growth rate, producing the most papers. This reflects China’s increasing focus on river and lake ecosystem health over the past 15 years, driven by policy initiatives such as “Happy Rivers and Lakes,” “Protection of the Yangtze River,” “Make the Yellow River a Happy River for the Benefit of the People,” and the “River Chief System” and “Lake Chief System” policies.

Figure 4 further detailed analysis of the top three high-productivity countries in this field. Chinese scholars led the field, contributing 619 papers, which accounts for 43.8% of the total publications. However, China had the lowest citation rate among these countries, indicating that the international recognition of Chinese scholars’ work still needs improvement. The United States ranked second, with 237 publications and 7303 citations. Canada, though producing fewer papers (114), had the highest citation rate, with 4391 citations, averaging 38.52 citations per paper, suggesting a strong impact of Canadian research in this field. This influence may be attributed to several factors, including Canada’s rich freshwater resources, strong environmental policies, and the contributions of leading scholars and institutions that have played a central role in advancing both theoretical frameworks and practical approaches in river and lake ecosystem health research.

3.4. Keyword Analysis

Keywords encapsulate the core ideas of a paper. Through keyword co-occurrence analysis, we can identify research hotspots in the field of river and lake health science. Using VOSviewer to generate a keyword co-occurrence network for 1412 documents, 73 keywords with a frequency of 30 or more were selected for visualization, as shown in Figure 5. Larger nodes represent more frequent keyword appearances, highlighting key research areas. The lines between nodes show the strength of association, with thicker lines indicating more frequent co-occurrence in the same documents. High-frequency keywords like River, Sediments, Lakes, Heavy Metals, Pollution, Water, Fish, Risk Assessment, Contamination, and Bioaccumulation represent key research topics in this field.

Keywords such as Heavy Metals, Pollution, Fish, and Risk Assessment highlight the primary focus of river and lake health research. This focus centers on studying the health of rivers and lakes by investigating heavy metal pollution in water bodies and conducting risk assessments [34,35]. These trends are also clearly visible in the density visualization and explosive words (Figure 5b and

Table 1. Analysis of River and lake health keyword emergence intensity from 1991 to 2024.

Keywords	Year	Strength	Begin	End	1991–2024
Lake Ontario	1994	5.72	1994	2016	▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂
Lake Erie	1996	4.58	1996	2006	▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂
Bay	1999	4.61	1999	2013	▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂
Exposure	2000	6.53	2000	2007	▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂
Fish	1993	6.63	2007	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂
Accumulation	2001	4.62	2008	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂
Polychlorinated Biphenyls	1992	5.67	2010	2015	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂
Organochlorine Pesticides	2011	8.75	2011	2016	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▂▂▂▂▂▂▂▂
Polybrominated Diphenyl Ethers	2013	5.47	2013	2019	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂
Residues	2013	4.66	2013	2016	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂▂
Copper	1998	4.70	2014	2016	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂▂▂▂
Personal Care Products	2017	5.65	2017	2020	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
Three Gorges Reservoir	2018	5.18	2018	2020	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂
Groundwater	2019	6.12	2019	2021	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂
Diversity	2000	4.97	2022	2024	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃

Note: The red segments in the chart represent the duration of keyword bursts (a significant increase in citation or occurrence frequency), while the blue segments indicate periods without significant emergence intensity.

).

Density visualization provides an overview of research concentration in key areas. Each point is color-coded based on surrounding element density, with red indicating higher density and green representing lower density. The density reflects both the number of surrounding elements and their significance. Explosive terms highlight emerging research hotspots over a specific period, helping to identify overall trends [36]. By analyzing burst time and intensity, we used CiteSpace to extract the top 15 burst words from the full sample covering 1991 to 2024 (Table 1). These explosive terms can be divided into three distinct stages. The first stage (1991–2009) is characterized by a focus on the geographical location of studies. Lake Ontario and Lake Erie emerged as the most frequently studied and earliest locations in river and lake health research. These two Great Lakes, situated on the border between Canada and the United States, align with earlier findings that the U.S. and Canada were pioneers in this field during its early stages [37,38,39]. The second phase (2010–2017) emphasized the impacts of emerging pollutants like pesticides, chemicals, and personal care products on river and lake health [40,41]. The third phase (2018–present) has focused on more integrated themes such as the Three Gorges Reservoir, groundwater, and comprehensive river and lake health. Chinese scholars have increasingly concentrated on the health of rivers and lakes, especially the Yangtze River.

3.5. River Health Assessment Index System

The core of evaluating river and lake health lies in establishing robust indicator system. Building on previous research and a thorough review of numerous related papers, both domestically and internationally, a dataset for the evaluation index system was created by identifying the most frequently used criteria and indicator layers. Statistics reveal that the four primary criteria—morphological structure, water quantity, water quality, and biological and social service functions—each account for over 15% of total occurrences (Figure 6a) and are the most widely used. To further explore the relationship between these criteria and the factors influencing river health, this study conducted a statistical analysis of the evaluation indicators within these criteria, including a discussion on the weighting of these indicators.

In the construction of the river evaluation indicator system, the key indicators in the morphological structure standard layer include: river longitudinal connectivity index, shoreline natural condition, riverbank width index, and the extent of illegal development and utilization of water body shorelines, all of which are prioritized based on their importance for river health management. The common indicators in the water quantity standard layer are: the degree of ecological flow/level satisfaction and flow process variability, with different weights assigned depending on regional water management priorities. The critical indicators in the water quality standard layer include: water quality level, sediment pollution status, and water self-purification capacity, with the relative importance of each indicator being influenced by regional pollution control priorities. In the biological standard layer, frequently used indicators include: benthic macroinvertebrate biological integrity index, fish retention index, bird status, and aquatic plant community status, with the relative weighting of these indicators depending on the specific ecological context. The main indicators in the social service function standard layer are: flood control compliance rate, water supply guarantee level, water quality compliance rate of river-based centralized drinking water sources, shoreline utilization and management index, navigation guarantee rate, and public satisfaction (Figure 6b), with each indicator’s weight reflecting its importance in local governance and service delivery priorities.

The Guangzhou River Health Scoring Table illustrates how weighted indices (e.g., 30% for “water” vs. 20% for “biology”) reflect management priorities [16]. Similarly, the Yangtze River Economic Belt health evaluation model assigns higher weights to economic factors, such as water supply guarantees and industrial water usage [42], reflecting the trade-offs between ecological protection and regional economic development. In the UK, the Environment Agency’s River Health Index (RHI) incorporates a comprehensive weighting system for indicators like biodiversity (40%) and water quality (30%), with regional adjustments based on local ecosystem vulnerability [43]. These examples demonstrate how weighting systems can be tailored to reflect specific management objectives and regional priorities, which significantly impact the outcomes of river health assessments. A critique of such weighting systems would enrich the discussion of assessment frameworks by providing a more nuanced understanding of how indicator prioritization influences management decisions and policy effectiveness.

In the construction of the lake evaluation indicator system, the morphological structure standard layer replaces the riverbank width index with the lake area shrinkage ratio. The indicators in the water quantity standard layer are similar to those in rivers. The water quality standard layer adds lake trophic state as a key indicator. In the biological standard layer, aquatic plant community status is replaced by phytoplankton density and coverage of large aquatic plants. In the social service function standard layer, the navigation guarantee rate is removed, and the remaining indicators are largely the same as those in the river system.

4. Research Methods for River and Lake Health

The study of river and lake health identifies the level of ecosystem health and the degree of damage to rivers and lakes by comparing the current state of river and lake health with anthropogenic health standards or the health of rivers and lakes in their natural state [44]. Understanding the concept of river and lake health both domestically and internationally, selecting appropriate research methods, and building a targeted evaluation index system are crucial steps in analyzing the health status of rivers and lakes.

Currently, research on river and lake health, both domestically and internationally, primarily focuses on evaluating river ecosystem health. The evaluation methods and indicator systems are generally categorized into three types: (1) Guided by the needs of decision makers on certain aspects of rivers and lakes, single-factor indicators such as water quantity, water quality, biology, habitat and socio-economics are selected to carry out river and lake health assessment research [45,46]; (2) A prediction model is constructed based on the measured data of benthic animal communities to reveal the health status of rivers and lakes [47]; (3) Based on single-factor indicators reflecting the health of rivers and lakes, multiple evaluation indicators are integrated into a comprehensive indicator system through mathematical models to obtain comprehensive evaluation results of river and lake health [48].

4.1. Single Factor Evaluation Model

The single-factor evaluation model of river and lake health refers to the evaluation of a specific indicator for a particular aspect of the river or lake. Commonly used single-factor evaluation methods include: (a) Water quality index evaluation method: The health status of rivers and lakes is reflected by measuring the concentration of water quality indicators such as nutrients, chemicals and suspended solids in rivers and lakes [49]. (b) Water quantity index evaluation method: The health status of rivers and lakes is revealed through water quantity indicators such as flow and water level [50]. (c) Bio-indicator evaluation method: Evaluating the health status of rivers and lakes by measuring indicators such as the species, number and density of aquatic organisms (such as zooplankton, fish and benthos) in the rivers and lakes [51].

The single-factor evaluation method is simple and easy to understand, offering a clear reference for the preliminary assessment of water body health [52]. Additionally, the single-factor evaluation method for the same indicator is comparable, allowing comparisons between different rivers and lakes and different time periods [53]. However, this method focuses solely on a specific indicator, which limits its ability to comprehensively assess the overall ecosystem. This narrow focus can lead to one-sided or uncertain results.

4.2. Prediction and Evaluation Model

Aquatic organisms play a key role in energy transfer and material cycling within river and lake ecosystems, effectively reflecting the environmental pressures these ecosystems face [54]. As a result, the integrity of aquatic organisms has gradually become an important technical tool for river and lake health assessments, particularly benthic fauna, which has become a focal point in research due to its specificity within ecosystem structure and trophic levels. The UK was the first to develop a predictive evaluation model (RIVPACS) based on benthic community characteristics, using it to conduct nationwide river and lake health assessments [55]. Following this, Australia developed its own model (AUSRIVAS) based on the characteristics of the country’s rivers and lakes, and conducted nationwide health assessments [56].

QUAL2K, developed by the US Environmental Protection Agency (EPA), is a water quality modeling tool primarily used to simulate pollutants, nutrients, and water quality changes in rivers and lakes. It focuses on parameters such as water flow, temperature, dissolved oxygen, nitrogen, and phosphorus. This tool helps assess the impact of human activities, such as agricultural and industrial discharges, on water quality and predicts the effects of various management measures on water quality improvement. By modeling the physical, chemical, and biological responses in water bodies, QUAL2K enables the analysis of relationships between water quality, ecosystem health, and management decisions. In contrast, SWAT (Soil and Water Assessment Tool), developed by the US Department of Agriculture (USDA) and Texas A&M University, is a hydrological and water quality simulation tool used to model processes such as water cycling, soil erosion, and nutrient loss within watersheds, and to assess the impact of these factors on river and lake health. SWAT is widely applied in watershed management, pollution source analysis, and ecological restoration, and is particularly suited for modeling long-term water quality changes and pollutant transport. It is ideal for complex watershed systems. Compared to QUAL2K, SWAT focuses more on long-term water quality and hydrological models at the watershed scale, while QUAL2K specializes in water quality modeling at the local water body level. China has also made notable progress in river and lake health assessments. For example, the Fujian Province standard (DB35/T 2096-2023) integrates hydrological and ecological models, providing a useful framework for evaluating trade-offs in the selection of assessment tools. This standard offers valuable guidance for decision-makers by balancing model applicability, data requirements, and computational capacity.

While predictive evaluation models have been crucial in advancing river and lake health research, they still have limitations [57]. These models require the selection of suitable reference sites, and identifying rivers and lakes that are minimally disturbed by human activity can be challenging. Moreover, data collection demands considerable human and material resources [51]. Additionally, the heavy reliance on numerical calculations may overlook the complexity of ecosystem evolution, potentially leading to biased results [58].

In summary, predictive evaluation models based on benthic communities can effectively reflect the impact of human activities on river and lake health. However, benthic organisms are influenced by both natural environmental factors and human activities, with varying degrees of impact depending on the type of human activity. This introduces certain limitations to the application of this approach.

4.3. Multi-Factor Comprehensive Evaluation Model

Multi-factor comprehensive evaluation model is based on single-factor indicators reflecting the health of rivers and lakes. Through mathematical modeling, it combines multiple evaluation indicators into a comprehensive system, providing an overall assessment of river and lake health [59].

Multi-factor integrated evaluation models offer comprehensive diagnoses of river and lake health issues, serving as valuable tools for sustainable watershed management [60]. At present, the main internationally recognized models include: Rapid Bioassessment Protocol (RBP) of the United States [61], the Riparian, Channel and Environmental (RCE) of Sweden [62], System for Evaluating Rivers for Conservation (SERCON) of the United Kingdom [63], River Health Programme (RHP) of South Africa [64,65] and Index of Habitat Integrity (IHI) [66], Index of Stream Condition (ISC) of Australia [67], and the EU Water Framework Directive (WFD) [10], among others.

In adopting the multi-factor comprehensive evaluation model, domestic scholars have conducted extensive research and practical applications, leading to the development of various algorithms for river and lake health assessments. These include neural network model [68], matter-element extension model [69], projection pursuit model [70], multivariate connection number model [71], TOPSIS model [72], fuzzy comprehensive evaluation model [73], gray correlation analysis model [8], set pair theory [74], multidimensional similarity cloud model [75] and Pythagorean fuzzy cloud model [48], to improve the applicability and accuracy of the model (Table S5). Although the multi-factor comprehensive evaluation model includes many river and lake health characterization factors, there are limitations to the approach [76]. A common issue is that comprehensive evaluations integrate individual indicators by weighting, which can result in high-scoring indicators compensating for lower-scoring ones. This can lead to inflated overall health scores, masking underlying issues in the river and lake ecosystems [77]. In addition, each evaluation index often responds to environmental pressure to varying degrees, and the comprehensive evaluation results may cause the information represented by some key factors to be hidden [78]. In general, the current research methods for river and lake health mainly include single-factor evaluation model, predictive evaluation model and multi-factor comprehensive evaluation model. Among these, the multi-factor comprehensive evaluation model has the most application research and occupies a dominant position.

A comparison of the above three types of river and lake health research methods is shown in

Table 2. Main international research methods on river and lake health.

Research Method	Main Content	Method Description	Advantages	Disadvantages	References
Single Factor Evaluation Model	Water quality index method: Includes single water quality indicators and comprehensive water quality indices.	Using water quality indicators to analyze pollution levels in the river.	Reflects the degree of pollution through observed water quality conditions.	Only reflects pollution levels and cannot reveal ecological issues.	[79]
	Water quantity index evaluation: Investigates water quantity and flow conditions.	Monitoring flow rate and water volume indicators to assess river health status.	Direct and easy to understand, low implementation costs.	Limited scope and lack of universality; subjective evaluation may cause bias.	[50]
	Biological index method: Calculates fish indices and evaluates aquatic organisms like plankton and benthic animals.	Using biological integrity indices to reflect aquatic organism population status to assess river health.	Reflects the relationship between aquatic organisms and the water environment.	Time-consuming and costly; sensitive to environmental interference.	[51]
Predictive Evaluation Model	Predicts river health using data from benthic organisms.	Using data from benthic organisms to construct predictive models to assess river health.	Strong theoretical and mathematical foundations; results are objective and reliable.	Predictive models tend to neglect benthic organism dynamics, resulting in uncertainty.	[55,56,58]
Multi-Factor Comprehensive Evaluation Model	Combines single evaluation results to obtain a comprehensive assessment of river health.	Integrating multiple indicators to obtain a comprehensive evaluation of river health status.	Comprehensive evaluation that fully reflects river health conditions.	Multi-index integration may overlook certain river health issues.	[48,60]

. The research progress on the health of rivers and lakes is presented in Table S4.

5. Critical Issues and Future Trends in Current Research

5.1. Critical Issues in Current Research

Currently, both domestic and international research on river and lake health has been conducted from multiple perspectives, including morphology, water quantity and quality, biodiversity, and social service functions. The importance of river and lake health assessment in water body management is well recognized, leading to the development of various research methods. However, traditional probabilistic risk models impose strict requirements on sample sizes, typically yielding reliable risk estimates only when the sample size is large. Given the often limited data in real-world situations, research needs to explore how to make preliminary health predictions and early warnings with a reduced number of indicators under data scarcity. Therefore, there is an urgent need to develop river and lake health risk identification methods suited to scenarios with limited data and incomplete sample spaces.

The construction of dams has disrupted the connectivity of rivers and lakes and damaged biological corridors. Historically, the focus has been on flood control, navigation, water supply, irrigation, and biological resource utilization, neglecting the natural connectivity of river and lake systems. Due to the combined effects of river and lake connectivity, random environmental factors, and the bounded rationality of decision-makers, health assessments inevitably involve significant uncertainty. Current evaluation methods, such as composite index models, fail to fully consider the cumulative effects of these factors. Thus, there is an urgent need to develop assessment theories that are better suited to the unique characteristics of rivers and lakes, particularly in uncertain environments.

Human activities and hydraulic infrastructure have altered the physicochemical properties of river water, making it crucial to account for the impact of these projects in health assessments. Furthermore, the region’s unique geography and climate conditions make river and lake ecosystems particularly sensitive to climate change, necessitating the evaluation of river health under future climate change scenarios. To better understand and address these impacts, it is essential to conduct in-depth analyses of the health status and response mechanisms of rivers and lakes before and after the construction of hydraulic infrastructure, as well as under future climate change scenarios, and to propose targeted health optimization and ecological restoration measures. Therefore, future research should focus on the following solutions to address these challenges.

5.2. Future Trends

In response to the identified issues, I propose corresponding solutions. Building on a systematic review of nearly 35 years of river health research, the next logical step is to integrate previous findings with the lake health assessment framework outlined in the “Guideline.” This should be done by considering the specific conditions of the study area and selecting key factors influencing river and lake health based on monitoring data related to watershed land use, riparian zones, water quality, water ecology, and social service functions. From this foundation, a suitable set of evaluation indicators can then be developed.

A crucial component of current ecological conservation practices is the optimization of ecological connectivity and the conduct of health audits for transboundary lakes, which are essential strategies for promoting the sustainable management of rivers and lakes. The National Ecological Connectivity Optimization Platform, an integrated platform combining multi-source data and models, significantly enhances the accuracy and scientific rigor of ecological connectivity assessments. By integrating diverse monitoring data, such as watershed land use changes, wetland degradation, river water quality variations, and species distribution, this platform offers in-depth analyses of ecological corridors, critical habitats for species, and ecological network structure optimization [80]. Additionally, the platform’s integrated ecological models, such as ecological network models and species distribution models, provide valuable insights for decision-makers, helping them evaluate and optimize ecological connectivity within watersheds and supporting data-driven policy implementation. This platform offers practical, actionable solutions for governments and management agencies, particularly in the face of climate change and human impacts, making it an essential tool for ecological restoration and conservation [81].

When addressing the health management of transboundary lakes, mandatory health audits serve as an effective mechanism to ensure ecological sustainability and foster regional cooperation. These lakes often encounter issues such as water quality degradation, ecosystem disruption, and resource competition, which underscores the necessity of a standardized health assessment system. Health audits should encompass various indicators, including water quality, biodiversity, and habitat conditions. A shared monitoring platform should be established through international cooperation to regularly assess the ecological state of these lakes [82,83]. By formulating international agreements or joint declarations, governments can be encouraged to adopt unified health assessment standards, enabling timely ecological restoration recommendations and policy adjustments. Regular health audits not only help to identify potential ecological risks early but also promote cross-border collaboration, facilitating shared water resource management and ecological governance within the region. These actions ensure that the health management of transboundary lakes can effectively address the challenges posed by climate change, land use alterations, and water resource management [84,85].

In addition to the current approaches, addressing the limitations in data availability and uncertainties associated with sample space is essential for advancing river and lake health assessments. Innovative methodologies such as cloud information diffusion theory and multi-source information fusion technology can be applied to effectively identify health risk factors and high-risk areas, providing a more scientifically sound model for river and lake health risk identification. Furthermore, a multi-dimensional river and lake health evaluation model can be developed by incorporating factors such as river-lake connectivity, hydrological dynamics, random environmental factors, and the bounded rationality of decision-makers. This model should address uncertainties across multiple dimensions, including hydrological dynamics, ecology, and water quality, offering a comprehensive understanding of the health of rivers and lakes. Considering the challenges in data collection and monitoring, the model design should focus on reducing both costs and the number of indicators. Additionally, the model should undergo predictive performance validation and comparison to enhance its accuracy. This methodology would introduce a new technological approach for rapid river and lake health predictions under data-limited conditions, enriching the tools available for river and lake health assessments.

Given the extensive presence of hydraulic infrastructure in the watershed, it is recommended to establish a hydrological-hydrodynamic-ecological model, coupled with the freshwater health index method, to analyze the impacts of future environmental changes on river and lake health. These changes could include pre- and post-dam construction effects, varying runoff reliability, land use changes, and climate change scenarios. Climate change, as a major source of uncertainty, influences hydrological cycles, precipitation patterns, and temperature, thereby affecting river flow, water quality, and habitat quality, which ultimately impacts ecosystem health. Land use changes and ecosystem degradation, such as wetland loss and river diversion, compromise river connectivity and stability, while water resource management practices, including over-extraction and irrational river diversion, can exacerbate water shortages and pose threats to river ecosystems. By comprehensively analyzing the impacts of human intervention, water resource availability, land use changes, and climate change on river health, a deeper understanding of river responses under various environmental conditions can be achieved, providing a scientific basis for future river and lake management and ecological protection.

6. Conclusions

River and lake health assessment is a technology that combines the knowledge of hydraulics and ecology with numerical simulation technology to evaluate and predict the impact of natural and human activities on rivers and lakes. This method establishes a new evidence-based approach in the field of water resource utilization and ecosystem impact assessment. This method has been proposed for more than 50 years and has attracted the attention of hydraulic and ecological experts. It has been widely used by researchers and river basin management agencies in various countries. In summary, the river and lake health model has the following advantages and disadvantages.

6.1. Advantages

River and lake health assessment is based on computer technology, which can effectively handle a large amount of hydrological, hydraulic and ecological data, and has the advantages of standardization, flexibility and easy interaction. The model is also highly adaptable, allowing integration not only with hydrodynamic models but also with water quality and ecological models, providing a more accurate reflection of river and lake health. This adaptability enables the evaluation of different flow allocation schemes and the development of tailored models to address specific challenges.

6.2. Disadvantages

Current research on river and lake health assessment lacks a standardized indicator system that can universally apply to all rivers and lakes due to the complexity and diversity of species and ecosystem conditions. Establishing a more accurate assessment framework and selecting suitable indicators is particularly challenging, especially for rivers and lakes in regions with little or no data, where monitoring and data collection are difficult. In such areas, historical data on river and lake health is often limited or nonexistent. Furthermore, insufficient research has been conducted on the combined effects of uncertain data, random environmental factors, and the limited rationality of decision-makers in the assessment process. Most domestic studies focus on the Yangtze and Yellow River basins, with limited attention given to southwestern rivers, inland river basins and international rivers. These also represent the directions for our future research.