Progress and future of China's aquatic ecological environment protection

Safeguarding water resources, aquatic habitats, and ecosystems is paramount for the well‐being of the populace, the future of the nation, and the sustainable development of China. With the relentless progression of ecological and environmental protection and the establishment of an ecological civilization, China's aquatic ecological environment protection has undergone five decades of exploration. The water environment protection paradigm has gradually transitioned from emphasizing pollutant emission concentration control and total pollutant emission control to prioritizing water environment quality improvement. Particularly in the past decade, regions nationwide have conducted proactive explorations and practices in source control, emission abatement, and quality enhancement. This paper systematically reviews the achievements in China's water environmental quality improvement and the characteristics of water environment management at various stages over the past half‐century. Considering the deployment of “three waters” coordination (water resources, water environment, and water ecology), green development, pollution, carbon reduction, and so forth, this paper analyzes the challenges confronted by China's aquatic ecological environment protection. Finally, future directions are prospected from six aspects: green development, climate change response, water resource allocation optimization, collaborative governance of multiple pollutants, aquatic ecological protection strengthening, and intelligent management improvement.


| INTRODUCTION
Water is the lifeblood of existence, the cornerstone of production, and the foundation of ecology.China's aquatic ecological environment protection officially commenced with the pollution control of Guanting Reservoir in Beijing in 1972, spanning over five decades.Water resources are crucial for people's well-being, the nation's future, and the sustainable development of China.On the basis of socioeconomic development, water resource and environment carrying capacity, water pollutant emissions, and other factors, China's water pollution prevention and control paradigm has gradually evolved from focusing on emphasizing pollutant emission concentration control to total pollutant emission control and then prioritizing water environment quality improvement (Wang et al., 2021;Xie, 2020).The water pollution control approach has transformed from targeting industrial pollution control to comprehensive source control, emission abatement, and systematic management.Water environment quality has improved significantly, with physicochemical indicators, such as BOD 5 , total phosphorus, and DO, reaching or approaching levels of moderately developed countries.However, disparities persist between China and developed nations in water resource security, aquatic ecology protection, meeting the requirements of building a beautiful China by 2035, and the growing ecological demands of the populace (Xu et al., 2021).Furthermore, the carbon peaking and neutrality goals announced by President Xi Jinping at the UN General Assembly present both opportunities and challenges for water environment management.Facing increasingly acute aquatic ecological issues, it is imperative to continuously adjust the concept of economic and social development, as well as water environment management and protection strategies.This study aims to systematically review the achievements in China's water environmental quality improvement and the characteristics of water environment management at different stages, analyze the current challenges faced, and provide an outlook on future directions.On the basis of the progress and effectiveness of China's water environment management over the last half-century, and aligning with the requirements of building an ecological civilization, green development, carbon peaking, and neutrality, this study analyzes current challenges and explores future research directions.The findings are crucial for formulating China's medium-and long-term path for enhancing the aquatic ecological environment and provide references for protecting and constructing beautiful river basins, rivers, and lakes.

| Changes in water quality
Figure 1 illustrates the changes in China's water quality from 1984 to 2023.In 2023, the proportion of Classes I-III water quality sections among the 3641 national control sections reached 89.4%, while inferior Class V sections accounted for a mere 0.7%.Compared with 1994, when water quality was at its nadir, China's gross domestic product (GDP) increased 24.9fold, Classes I-III sections increased by 64.1 percentage points from 25.3% to 89.4%, and inferior Class V decreased by 34.6 percentage points from 35.3% to 0.7%; major pollutant concentrations have greatly diminished, with permanganate index decreasing from 9.98 to 3.01 mg/L (69.8%) and ammonia nitrogen decreasing from 2.19 to 0.18 mg/L (91.9%).The "China's Ten Years" report card released by the Publicity Department of the CPC Central Committee highlights that the decade since the 18th National Congress has witnessed the most strenuous efforts and most remarkable results in aquatic ecological environment protection (Ministry of Ecology and Environment, 2022).

| Progress in water environment treatment and protection
Figures 1 and 2 demonstrate that China has undergone a process of pollution followed by treatment.Key initiatives such as industrial pollution control, prevention and control in key river basins, and defending clear waters have been carried out successively.The water environment treatment concepts have evolved over three stages.
Interception of pollution treatment, focusing on industrial pollution : The 1972 fish pollution incident at Guanting Reservoir in Beijing garnered national attention about water pollution.During this period, pertinent policies including the "Water Pollution Prevention and Control Law," "Environmental Quality Standards for Surface Water," and "Integrated Wastewater Discharge Standard" were promulgated; the "three policies" and "eight systems" laid the groundwork for China's environmental management framework.However, due to a lack of macro-level coordination between economic development and environmental protection, the focus was on closing, relocating, and treating industrial pollution sources to meet discharge standards, while urban sewage treatment and comprehensive basin pollution prevention were not prioritized.Despite requiring industries to implement discharge standards, weak environmental supervision resulted in poor compliance.Water environment quality deteriorated nationwide, truly portraying "all rivers polluted, all waters contaminated." Changes in the proportion of national surface water sections and gross domestic product .
Source control and emission reduction, promoting water quality improvement (1996-2012): From the "Ninth Five-Year Plan" to the early "Eleventh Five-Year Plan," with economic growth, population increase, rapid urbanization, and industrialization, water pollutant discharges far exceeded environmental capacity.In August 1996, the State Council proposed "one control and double standards" (controlling total emission of major pollutants, meeting standards for industrial pollution sources and environmental quality by function zones in key cities), adopting a capacitybased total control approach ahead of its time.During the "Tenth Five-Year Plan," water environment quality was not fully contained as incremental pollution exceeded reductions.In the "Eleventh Five-Year Plan," China implemented a stringent water pollutant total emission control system, making it a binding indicator for government assessment.
To continuously reduce total water pollutant discharges, China tightened emission standards.Shandong Province issued basin emission standards to control pollution from papermaking, brewing, chemical, textile, and dyeing industries; in 2006, Class A standards of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant" were implemented for plants discharging into key water bodies.Beijing required effluents to meet quasi-Class IV surface water standards.China has issued 46 local water pollutant comprehensive emission standards and many basin standards, such as the "Comprehensive Discharge Standard for water pollutants in the Nansi Lake Basin." Nationally, environmental infrastructure construction was promoted.By 2022, urban sewage treatment reached 21.606 billion tons/day (Xie, 2020), transforming from a "scale growth" model emphasizing facilities over pipe networks to "quality and efficiency improvement" (Qu et al., 2019).Deep treatment and clean transformation of key industrial sectors were advanced; centralized treatment facilities were completed in approximately 2600 industrial parks.Rural sewage and livestock/poultry waste treatment were promoted.
Through rigorous total emission control in the "Tenth" and "Eleventh Five-Year Plans," chemical oxygen demand (COD) and ammonia nitrogen discharges decreased significantly.Figure 2 shows that by the early "Twelfth Five-Year Plan," major pollutant concentrations approached Class III surface water levels, enabling a shift from emission reduction to quality improvement.In the "Thirteenth Five-Year Plan," a quality-centric treatment approach emerged, linking reduction projects with quality improvement requirements, advocating precise and scientific control, and supervising pollution sources, outfalls, and receiving waters.The "Eleventh" to "Thirteenth Five-Year Plans" saw a cumulative COD reduction of 6.426 million tons, contributing to water quality improvements.
Water quality improvement and systematic treatment (2013-present): Since the 18th National Congress, ecological civilization was incorporated into the "five-in-one" layout; continuously promoting ecological progress is a key part of this endeavor.In 2013, public opinion events like "letting the environmental protection bureau director swim in the river" and issues of water shortages, serious pollution, and ecological degradation caused great social repercussions.The 2015 "Water Pollution Prevention and Control Action Plan" ("Water Ten Articles") marked a historic turning point in the protection approach, systematically promoting pollution prevention, ecological conservation, and resource management (State Council, 2015).It focused on quality, coordinated pollution control, industrial transformation, and water resource conservation, insisted that conservation means reduction, and emphasized integrated management of water quality, quantity, and ecology.This groundbreaking initiative laid the foundation for "three waters" coordination in the "Fourteenth Five-Year Plan." The 2018 institutional reform established the Ministry of Ecology and Environment (MEE) to uniformly regulate the ecology and environment, separating ownership and supervision for independence and cooperation (Zheng, 2018).The "Water Ten Articles" clarified responsible units and departments; relevant ministries fulfilled respective duties and actively explored.A working pattern of joint responsibility and combined posts emerged.The reform moved water function zoning and outfall supervision to the MEE, realizing unified oversight of above and below F I G U R E 2 Changes in water pollutant concentrations .
ground, shore and water, land and ocean, urban and rural, achieving "four breakthroughs" and initially resolving the "nine dragons ruling the water" issue.
To meet the 2020 goal of building a moderately prosperous society, water quality target management was further strengthened.China's administrative system consists of central government and provinces, cities, counties, and townships (Deng et al., 2016).To strictly implement local responsibilities, the assessment of water quality and total pollutant emission control targets in key basins from the "Eleventh Five-Year Plan" was expanded from 22 to all 31 provinces.Assessment indicators increased from permanganate index and COD to 21 indicators of "Environmental Quality Standards for Surface Water"; water quality assessment sections increased from 157 in 2009 to 3641.During the "Water Pollution Prevention and Control Action Plan," the MEE signed target responsibility letters with 31 provincial governments, greatly promoting precise, scientific, and law-based pollution control.These measures have fully demonstrated the advantages of China's political system (Table 1).
China also established potent systems, such as central ecological and environmental protection inspections, to investigate and deal with major ecoenvironmental damage cases.The literature demonstrates that these inspections can effectively solve problems by implementing government and enterprise responsibilities and resolving public demands, significantly reducing transboundary water pollution, especially in eastern developed regions and tributaries (Lu, 2022).

| CHALLENGES FACED
Despite remarkable progress in water pollution prevention and control, the rapid intensification of climate change and human activity impacts has led to the emergence of severe aquatic ecoenvironmental problems and crises, such as unbalanced and uncoordinated water quality improvement (Xu et al., 2021), dried-up riverway (Li et al., 2022;Xu et al., 2021), biodiversity decline (Yin et al., 2022), and so forth.These have become key factors restricting regional economic and social development and ecological and environmental protection (Wang & He, 2022).

| Contradiction between development and protection
China completed the world's largest-scale urbanization and industrialization in five decades, supporting the process with extremely limited water resources.Correctly handling the relationship between economic development and environmental protection is of great significance to the development of China's water environment protection (Huang et al., 2021;Yin et al., 2022).Since 2000, the coordinated development of China's economy and environment has improved to some extent, with the eastern region exhibiting a higher degree of coordination than the western region (Fang et al., 2023).
The 19th Central Committee's Fifth Plenary Session in 2020 proposed promoting the comprehensive green transformation of economic and social development, pointing out that the current domestic situation of a heavy chemical industry-dominated structure and resources and environment carrying capacity reaching or nearing the upper limit has not fundamentally changed.This leads to relatively large root pressure on ecological and environmental protection, with the coordinated development of ecology, environment, economy, and society remaining a major future challenge.Ecological civilization is an important direction for China's future development, aiming to seek technological and scientific solutions to pollution and ecological degradation amidst sustained economic growth (Hansen et al., 2018).To this end, in 2016, China proposed the strategy of "jointly promoting great protection and On the basis of the State Council's government work report, China's GDP growth rate remains around 5% each year.Under constraints such as the red line of China's total water use and the requirement that water environment quality "will only get better, not worse," plus the requirements of carbon peaking and carbon neutrality, green development is the fundamental strategy for maintaining continuous economic development, continuously improving the ecological environment, and solving pollution problems (Xu et al., 2022).The water-related fields of development and protection still face many profound challenges, including how to improve the level of cleaner production and pollution abatement in industrial manufacturing, how to continuously promote nitrogen and phosphorus reduction while ensuring food security as a global problem for nonpoint source governance, and how to collaboratively reduce pollution and carbon emissions in water pollution source control to increase effectiveness.These challenges all require cooperation between the ecological and environmental departments and the economic development and science and technology departments to jointly study and promote plans for industrial green development and the research and development of green and low-carbon technologies for key industrial sectors (Xia, 2021).

| Contradiction between water resource development and utilization and ecological wateruse guarantee
The "National Comprehensive Water Resources Plan" has set a control target that the total national water use should strive to be controlled within 700 billion m 3 by 2030.Since 1997, China's total water supply and total water use have grown slowly and have basically remained stable since 2013 (Qiu et al., 2023).The total water use in 2022 was 599.82 billion m 3 .In the allocation of water resources, although the proportion of agricultural water use and industrial water use has decreased to a certain extent, they still remain above 60% and 15%, respectively.In 2022, ecological water use accounted for a mere 5.7% (Zhen et al., 2023), which is still relatively low, and the water-use structure needs to be optimized.In some regions, the contradiction between resource-based water shortages and high water-consuming development models has long coexisted.For example, the per capita water resources in the Yellow River Basin are less than 500 m 3 , which is a relatively scarce water resource area.The water resource development and utilization rate in the Yellow River Basin has reached 73% (the internationally recognized warning line is 40%), but at the same time, the Yellow River Basin is also an important energy and coal chemical industry base in China, with the number of coal chemical industry enterprises accounting for about 80% of the country.It is extremely challenging to ensure ecological water use in rivers and lakes in this region.
According to the "2018 National Water Conservancy Development Statistical Bulletin," 104,403 sluice gates have been built on rivers with a flow rate of 5 m 3 /s or above nationwide.Unreasonable water resource allocation, regulation, and hydropower development have led to the widespread phenomenon of cut-off and drying up of small and medium-sized rivers.At present, interbasin water diversion is considered a feasible strategy to solve the problems of water resource shortage and water quality degradation (Song et al., 2023).However, in the implementation of engineering water volume regulation with the basin, most projects have not considered ecological water use or only considered ecological base flow, threatening the ecological security of the basin (Qiu et al., 2023).Since 2020, the Ministry of Water Resources has issued four batches of ecological flow guarantee targets for key rivers and lakes, covering 171 interprovincial key rivers and lakes and 286 control sections nationwide, but the overall coverage is still far too low.The Ministry of Water Resources has issued the "Technical Specification for Calculation of Water Demand for River and Lake Ecological Environment," but the current problem is that the ecological base flow of rivers and lakes based on relevant technical specifications is calculated under certain hydrological conditions and is often small, which is insufficient to support the needs of aquatic organisms in rivers and lakes.For each river basin and each river and lake, how to scientifically determine the ideal state of the "three uses" water-use structure within the basin, and how much water is actually needed for the hydrophilic needs of the people in the construction of a beautiful China, is the demand problem that needs to be solved first for ecological water-use guarantees.

| Nonpoint source management gaps and new pollutants neglected
Nonpoint source pollution prevention and control is a global problem.Even the Rhine River Basin, which has extensive experience in basin management, has not yet been thoroughly resolved, and China is no exception.After China implemented the total control system, point source emissions have shown a stable or declining trend, and the problem of concentrated inflow of nonpoint source pollutants into rivers during the flood season has become increasingly prominent.From the monthly water quality in recent years, the water quality is worse during the flood season from June to August each year, and urban and rural nonpoint source pollution has become the biggest challenge facing water quality improvement.Starting in 2022, the MEE has released a list of the top 50 sections with the highest intensity of pollution sources in China's surface water during the flood season, in the hope of alleviating the problem of urban and rural nonpoint source pollution through environmental supervision.
Due to China's stage of socioeconomic development, control standard system, and periodic characteristics of water environment governance, compared with developed countries, we still face the problem of new pollutant treatment.New pollutants pose major risks to human health and ecosystems.Relevant literature shows that new pollutants (including endocrine disruptors, perfluorinated compounds, microplastics, etc.) in China's water environment are widely distributed and exist in most regions.The maximum pollution levels of endocrine disruptors, perfluorinated compounds, microplastics, and so forth are far higher than the pollution levels in developed countries.Due to insufficient attention paid to new pollutants in the past and the lack of effective monitoring technologies for large-scale monitoring of new pollutants, China still faces the difficulty of unclear base numbers of new pollutants (Liu et al., 2021).The current water quality standards have limitations in regulating these emerging contaminants.

| Contradiction between severe damage to aquatic ecology and lack of top-level management policy design
Since the 1950s, human activities (overfishing, water pollution, water conservancy project construction, shipping and shoreline development, invasive alien species, etc.) have greatly altered the hydrological and ecological conditions of the Yangtze River Basin, and aquatic biodiversity has plummeted (Yin et al., 2022).Literature research shows that the causes of the Yangtze River biodiversity crisis, dams, hydropower stations, and other water conservancy projects have "contributed" 70% (The Nature Conservancy, 2021); the obstruction of the river and lake water systems has had an immense adverse impact on the aquatic ecological system.There is a substantial disparity between China's aquatic ecological protection and that of developed countries.Developed countries have currently entered the evaluation and management stage with aquatic ecological conditions as the core.The regulatory requirements for monitoring, evaluation, and management are relatively standardized, and the aquatic ecological conditions have surpassed the historical nadir and are gradually recovering (Xu et al., 2021).The "EU Water Framework Directive" has constructed a comprehensive aquatic ecological environment quality evaluation system, including "three waters" indicator.The United States takes water functional management as the basis and aims to protect human health and the safety of aquatic organisms.In contrast, China is currently in the incipient stage, lacking relevant standards and norms, with unclear base numbers, and the deteriorating trend of species diversity loss has not been effectively curbed.Recently, China has introduced a "ten-year fishing ban" measure for the Yangtze River (General Office of the State Council, 2024), demonstrating the Chinese government's determination to protect biodiversity.
Overall, China lacks a whole-chain and systematic toplevel design for the monitoring, evaluation, protection, and restoration of aquatic ecology.In terms of monitoring and evaluation, there is a dearth of a nationally unified and comparable assessment system (indicator weights, evaluation standards, etc.) (Su et al., 2023).Although the "Aquatic Ecological Environment Protection Plan of Key River Basin" proposes target requirements for 2025, including aquatic biological integrity indicators and task indicators for the construction of ecological buffer zones, artificial wetlands, and restoration of large aquatic vegetation, this plan clearly states the principle of "ecology first and natural restoration," but due to the lack of quantitative analysis of the mechanism, it is possible that engineering measures can help solve aquatic ecological and environmental problems, but the implementation of the project maybe also cause adverse effects (Sheng et al., 2022).

| Collaborative and efficient systematic governance system needs to be improved
The "14th Five-Year Plan" is a transition period from water pollution prevention and control to systematic governance of river basin elements, such as water resources, water environment, and aquatic ecology.From the perspective of a beautiful China, the scholars conducted a coordination evaluation of water resource-water environment-aquatic ecology indicators in Chinese cities (Guan et al., 2024).The research shows that overall, although the coordination between water resources and the water environment has shown an upward trend, the coordination between aquatic ecology and the other two systems has shown a downward trend.The pattern of "three waters" coordinated systematic governance is still in the initial exploration stage, and the goals and tasks of aquatic ecological environment protection have not yet been coordinated and unified.Further efforts are needed to break down departmental barriers and establish a collaborative mechanism.
The previous pollution prevention and control work, which is centered on quality improvement, has not fully coordinated the needs for pollution reduction and carbon reduction (Zhang et al., 2023).In 2020, China proposed the dual carbon goals.Therefore, while managing the whole chain of water environmental protection from "pollution source-river outfall-receiving water body," it is also necessary to fully consider measures and projects to reduce greenhouse gas emissions and strive to achieve collaborative governance of water pollution reduction and carbon reduction.According to preliminary calculations using the method of the United Nations Intergovernmental Panel on Climate Change, in 2019, the greenhouse gas emissions of China's sewage treatment industry could reach 48.7 million tCO 2-eq , and the carbon emissions from sewage treatment represented by industry, agriculture, and domestic sources account for 1%-2% of China's total carbon emissions (Xie & Wang, 2012).The methane emissions from industrial wastewater treatment, urban sewage treatment plants, livestock and poultry breeding, and so forth, still show an increasing trend (Du et al., 2023;Li et al., 2013;Ramírez-Melgarejo et al., 2020).
Recently, the Chinese government issued the "Opinions of the Central Committee of the Communist Party of China and the State Council on Comprehensively Promoting the Construction of a Beautiful China," requiring the completion rate of beautiful rivers and lakes to reach 40% by 2027, involving a list of 2573 rivers and lakes (Ministry of Ecology and Environment, 2023).The problems of imbalance and uncoordinated development in various places are prominent, and the spatial heterogeneity is large.How to make the tasks of pollution reduction, carbon reduction, ecological protection, new pollutant treatment, and so forth, play the best comprehensive benefits and reach the beautiful requirements as soon as possible.In particular, it is a huge challenge to the construction of beautiful rivers and lakes through precise pollution control and protection.

| FUTURE DIRECTIONS OF CHINA'S AQUATIC ECOLOGICAL ENVIRONMENT PROTECTION
China's economic and social development and aquatic ecological environment are different from other countries, and the experience of developed countries cannot be completely copied (Gao et al., 2008).At present, relevant policy documents in China have clearly stated the target requirement, "by 2035, the ecological environment will be fundamentally improved and a beautiful China will be basically built."China must develop strategic measures that suit its national conditions and meet the specific needs of solving aquatic ecological environment problems.

| Adhere to green development to promote harmony between humans and water
The coupling between socioeconomic systems and aquatic ecological environment systems is becoming increasingly profound, and ecological and environmental problems are closely related to economic development models.How to balance the relationship between development and protection is an eternal theme of human development and ecological and environmental protection.Only by standing from the perspective of harmony between humans and water, accelerating the formation of green production methods, green lifestyles, and green consumption patterns, and accelerating the transformation of development modes toward greening and low-carbon, can we effectively reduce the high dependence on resources and environment in the development process, lower the level of pollutant generation and emission, achieve a win-win progress of high-quality development and high-level protection, and continuously enhance the people's sense of gain, happiness, and security.
The current in-depth battle against pollution is based on the present and focuses on solving key aquatic ecological and environmental problems around the people, but at the same time, it must also have a long-term vision and combine with the goal of building a beautiful China by 2035.Green development is the fundamental path to realizing the beautiful scene of "clear waters, green shores, and fish swimming in shallow waters" in rivers and lakes in the future.It is necessary to carry out research on green basin construction technology, research on the coupling and feedback mechanism of the "human-water" relationship, explore the evolution and protection mechanism of the water environment under the influence of human activities, and construct a coordinated path of development and protection.

| Improve the adaptability of aquatic ecological environment protection to climate change
Human activities have caused a large amount of greenhouse gas emissions, leading to a gradual increase in the frequency and intensity of hydrological and climatic events, such as extreme droughts and heavy rainfall.Many scientific studies have linked extreme hydrological events to climate change and predict that extreme droughts, heavy rainfall, and other events will be more intense and frequent in the future (Jef et al., 2018;Melissa, 2023).Under the influence of climate change, profound changes will occur in river and lake aquatic ecosystems.In July 2022, the continuous highintensity extreme drought event in the Yangtze River Basin made it difficult to maintain the necessary ecological water level of lakes and reservoirs.Coupled with the continuous high temperature and heat, it caused water quality deterioration, bringing significant impacts on the living environment of aquatic organisms, shrinking the living space of wild fish, Yangtze finless porpoises, and other rare aquatic organisms, and reducing the function of river, lake, and wetland aquatic ecosystems (Xia et al., 2022).For lakes with shallow water and high eutrophication levels, the maximum growth rate of many cyanobacteria that can form blooms is usually higher than 25°C, and nutrients and temperature have a synergistic effect on cyanobacterial growth.In the future, with climate warming, it may be necessary to further reduce nutrients while inhibiting the growth of cyanobacterial blooms (Jef et al., 2018).
Facing rapid climate change, strengthening the adaptability of rivers and lakes is the better way to avoid harm.From a macro perspective, research should be conducted on the impact of climate change (extreme weather events, such as rainstorms and droughts) on the quality of the aquatic ecological environment, and corresponding adaptive management policy research should be carried out.For rivers with water conservancy projects, the impact of extreme weather events on the upstream and downstream water quality and aquatic ecological environment of water conservancy projects should also be analyzed simultaneously (Xia et al., 2012), so as to minimize the adverse effects of climate change and promote sustainable development of the region in a changing environment.Nature-based solutions and ecoenvironmental infrastructure can play important roles in enhancing the resilience of aquatic ecosystems to climate change.

| Reset the "three uses" water-use order and optimize water resource allocation
Fully consider the relationship between water resource allocation and high-quality economic development and aquatic ecological environment protection, with the goal of maintaining the function of river and lake ecosystems, and in accordance with the requirements of the "Yangtze River Protection Law," the "Yellow River Protection Law," and other regulations, enhance the status of ecological water use in water resource allocation and optimize the structural proportion of production water use, domestic water use, and ecological water.In water-scarce regions, water resources should be regarded as the biggest rigid constraint.For each river basin, it is necessary to conduct indepth research on how to balance the needs of ecological water use and socioeconomic water use, adhering to the principle of determining cities, land, people, and production based on water.Urban development layout, agricultural planting structure, domestic water-use habits, and production water-use methods are determined according to the available amount of water resources.In addition, reuse of nontoxic and harmless wastewater as ecological water back into water bodies should be encouraged.
The "Yangtze River Protection Law" and the "Yellow River Protection Law" stipulate that for water conservancy and hydropower projects, shipping hubs, and other projects upstream of the mainstream, important tributaries, and important lakes, ecological water dispatch should be incorporated into the daily operation dispatch rules, and a routine ecological dispatch mechanism should be established to ensure the ecological flow of rivers and lakes.Case studies show that in 2023, the ecological dispatch management of the Three Gorges Reservoir can significantly improve the spawning habitat quality of the four major Chinese carps in the Gezhouba to Zhijiang river section, and the area suitable for spawning the four major Chinese carps will increase significantly (Bai et al., 2024).Therefore, an ecological dispatch mechanism should be established as soon as possible to coordinate the relationship between upstream and downstream, mainstream and tributaries, and deepen the connection of river and lake water systems and the ecological dispatch of water conservancy and hydropower projects.Especially in the dry season, based on the needs of aquatic organisms, the response relationship between river flow, water quality, hydrodynamics, and reservoir operation should be established, and the ecological water-use guarantee rate of rivers and lakes should be improved by optimizing reservoir operation rules (Ai et al., 2022).Integrated water resources management and basin-scale planning are crucial for optimizing water allocation and ecological conservation, as exemplified by the Yangtze River Economic Belt and Yellow River Basin plans.

| Deepen collaborative governance and efficiency enhancement of multiple pollutants
At present, China's water pollution source control faces new situations, such as carbon peaking and neutrality, collaborative efficiency enhancement of pollution and carbon reduction, and new pollutant treatment.On the basis of conventional pollutant control, the requirements of carbon reduction and risk prevention and control for human health should be added, and a collaborative technology system of "carbon reduction-pollution reduction-health" should be developed through coupling (Huang et al., 2024).On the basis of the interaction of multiple elements and media, interdisciplinary research should be carried out to coordinate the collaboration of multiple pollutants, the treatment of traditional pollutants and new pollutants, pollution reduction and carbon reduction, land and ocean, surface and underground, and establish a comprehensive prevention and control system covering the collaboration of multiple pollutants.For example, regarding the requirements of carbon reduction and new pollutant treatment, it is urgent to coordinate and exert synergistic effects in the process of implementing conventional industrial, domestic, and agricultural pollutant emission reduction policies to maximize the overall benefits of pollution and carbon reduction.Another example is the currently prevalent nature-based solutions (such as constructed wetlands), which are sustainable, low-cost, and low-energy solutions aimed at using natural processes for water pollution treatment.This measure is often regarded as a single water environment treatment action, but at the same time, a large number of studies have shown that this measure can further tap the potential of carbon reduction and fully exert its synergistic effect of pollution and carbon reduction.
For environmental decision-makers, innovative technologies and management strategies should be proposed for controlling multiple pollutants and reducing greenhouse gas emissions from wastewater treatment.In the process of coordinating the management of multiple pollutants, it is necessary to focus on researching "what needs to be coordinated," "where to coordinate," "how to coordinate," and "what measures are needed to ensure coordination," including the coordination of treatment objects, treatment indicators, spatial scope, task measures, and so forth.And then, integrating policies, such as "total amount control" and "pollutant discharge permit," a joint prevention, control, and treatment mechanism should be built to promote the collaborative efficiency enhancement of treatment and protection.

| Strengthen the construction of an aquatic ecological protection management system
After completing two phases of treatment actions, the Rhine River is currently implementing the "Rhine River Action Plan (2021-2040)," which adopts more comprehensive measures to restore the river ecosystem from the perspective of harmony between humans and nature, including protecting wetlands, opening nature reserves in the delta region, removing dams on tributaries, or setting up fish passages (International Commission for the Protection of the Rhine, 2020).Aquatic ecological protection and restoration in China is just starting.National standards for aquatic ecological monitoring, investigation, and evaluation should be introduced as soon as possible, the aquatic biological monitoring network should be improved, and basic work such as investigation and assessment should be accelerated to grasp the dynamic changes of important aquatic organisms, summarize the indicative species of each river basin, and construct an aquatic ecological protection list for each river basin.Upholding the concept of respecting nature, conforming to nature, and protecting nature, and following the principle of "protection first and natural restoration as the main approach," an aquatic ecology-oriented protection management goal and implementation path should be established.It is particularly important to note that the implementation path, based on the principle of feasibility, actively promotes aquatic ecological protection and restoration measures that are conducive to the protection of aquatic ecosystems and carry out shoreline restoration and aquatic organism habitat restoration according to local conditions.The need for strengthening monitoring, assessment, and regulation of aquatic ecological health and biodiversity conservation should be emphasized.

| Improve the level of integrated intelligent management of the ecological environment
With the deepening connection between water and related systems, such as food, energy, health, and economy, the transmission of ecosystem materials, energy, and information is constantly changing (Long et al., 2020).How to improve the comprehensive management capacity of the basin's ecological environment system has become a new issue that needs attention.Promote the research and development of space-air-ground integrated intelligent sensing technology, integrate data from relevant departments, such as ecological environment, water conservancy, agriculture, ocean, and forestry and grass, establish a big data platform for aquatic ecological environment.Research and develop "three waters" integrated simulation technology, multiprocess coupling and interaction of "hydrology-hydrodynamics-water quality-aquatic biology," and the coupling feedback mechanism of "waterenergy-food-ecology," and build an integrated decisionmaking system for basin ecological environment management.Systematically promote multidimensional correlation analysis and early warning analysis of section water quality, river outfalls, pollution sources, biodiversity, habitat conditions, water resources, and so forth, to help achieve precise decision-making on problems, time, location, objects, and measures in aquatic ecological environment treatment.

| CONCLUSION
Humans live by water and civilization thrives because of water.Although significant results have been achieved in improving water environment quality over the past halfcentury, we are also facing challenges such as a weak aquatic ecological foundation and a multielement, crossmedia systematic governance pattern that has not yet been formed.There are still many unknown influences of climate change, rapid economic development, and other factors on the river and lake ecological environment system.Facing challenges, we need to grasp and study macro laws and medium-and long-term impacts, and at the same time, we need to establish more precise, scientific, and law-based precision pollution control technologies and methods.Solving aquatic ecological environment problems requires long-term efforts.We must continuously explore new technologies for basin systematic governance and protection, strengthen policy coordination and task collaboration among relevant government departments, and adopt systematic governance models to achieve the best comprehensive benefits.The construction of a beautiful China with harmonious coexistence between humans and water is a long-term process that requires unremitting efforts.
Water environment quality assessment in different periods.Huai, Hai, and Liao) and two key lakes (Taihu and Chaohu), the Three Gorges Reservoir and its upstream, Songhua River, and the middle and upper reaches of the Yellow River, with a total of 157 sections COD (or Permanganate Index), NH 3 -N; total nitrogen and total phosphorus for the lakes T A B L E 1