Sewage, runoff, and unchecked urban growth degrade India's water bodies and threaten water security.
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Cities often grow faster than the systems designed to support them. As roads expand, buildings rise, and populations increase, urban lakes are frequently left to absorb the consequences. They receive sewage, stormwater runoff, sediments, and pollutants while continuing to provide ecological, social, and hydrological benefits to the communities around them.
For many residents, lakes remain sources of recreation, cultural identity, groundwater recharge, and in some cases, domestic water use. Yet the health of these water bodies is rarely monitored with the urgency they deserve.
A recent peer-reviewed study titled “Comparative assessment of seasonal dynamics in water characteristics of Salim Ali Lake and Harsul Lake in Chhatrapati Sambhajinagar, Maharashtra” (Lavhale et al., 2025) offers a technically rigorous and policy-relevant diagnosis of this crisis. Based on systematic sampling across four seasons in 2024, the study provides rare comparative insights into how urbanisation gradients influence lake health and why incremental interventions may no longer suffice.
Two lakes, two urban realities
The study focuses on two hydrologically connected lakes with very different surroundings. Salim Ali Lake lies within the densely built urban core of Chhatrapati Sambhajinagar. Harsul Lake is located on the city's periphery and is surrounded by a relatively less urbanised landscape. This contrast forms the foundation of the study.
Researchers assessed water quality using physicochemical parameters, heavy metal analysis, and widely accepted indicators, including the Water Quality Index (WQI), Coefficient of Variation (CV), and Nemerow Pollution Index (NPI). To understand how activities within the watershed influence lake health, they also used geospatial techniques such as watershed delineation through SRTM DEM and land use classification using Sentinel 2 imagery.
The results reveal a clear pattern. Salim Ali Lake consistently experiences higher pollution levels across all seasons, while Harsul Lake, although relatively healthier, is also showing signs of degradation. The difference reflects broader land use and urbanisation patterns rather than isolated pollution events.
Pollution changes with the seasons, but the problem remains
One of the study's most important findings is that lake pollution is dynamic. Water quality changes with rainfall, runoff, land use activities, and human pressures throughout the year.
The Nemerow Pollution Index shows that Salim Ali Lake remains heavily polluted in every season, with values ranging from 1.07 to 1.39. Even during winter, when runoff is generally lower, the lake records an NPI value of 1.17, indicating persistent contamination.
Harsul Lake performs somewhat better during the pre-monsoon period, with an NPI value of approximately 0.83. However, pollution levels increase during the monsoon and post-monsoon seasons, demonstrating the influence of runoff and pollutant loading from the catchment.
The Water Quality Index reinforces these findings. Salim Ali Lake frequently records WQI values above 100, placing it in the category of water unsuitable for use. During the monsoon, the WQI exceeds 150, indicating severe contamination. Harsul Lake fluctuates between good and very poor water quality depending on season and location.
What are the key pollutants affecting the lakes?
Several water quality parameters stand out.
Rising turbidity
Turbidity levels regularly exceed permissible limits. Values often reach 25 NTU compared to the standard limit of 5 NTU. High turbidity indicates increased sediment inflow, organic matter accumulation, and wastewater discharge. Elevated turbidity can reduce light penetration, affect aquatic life, and degrade overall ecosystem health.
Signs of nutrient enrichment
The study found pH values reaching as high as 9 in Salim Ali Lake, suggesting eutrophication driven by nutrient enrichment. Nutrients such as nitrates and orthophosphates, although sometimes remaining within permissible limits, point to ongoing pollution from sewage and agricultural runoff. Excess nutrients can stimulate algal growth and reduce dissolved oxygen levels in water bodies.
Heavy metals require attention
Copper was detected across seasons in both lakes. Although concentrations remained within permissible limits, the study highlights concerns about long-term accumulation in sediments. Over time, contaminated sediments can become secondary sources of pollution, affecting aquatic ecosystems and water quality.
Why the catchment determines lake health
The study's geospatial analysis helps explain why the two lakes differ so significantly. Land use and land cover mapping showed that approximately 22.5 percent of the watershed consists of built-up areas. Salim Ali Lake is almost entirely surrounded by urban infrastructure, while Harsul Lake retains greater vegetation cover and agricultural land within its catchment.
Urban landscapes generate large volumes of untreated sewage, solid waste, and polluted stormwater runoff. The study documents direct discharge of domestic wastewater into Salim Ali Lake, highlighting the consequences of urban infrastructure failing to keep pace with city expansion.
Harsul Lake remains comparatively protected but is increasingly affected by agricultural runoff, soil erosion, and expanding peri-urban development. The lake also receives inflows from multiple streams, making pollution management more complex because sources become dispersed across the catchment.
Beyond diagnosis: What needs to change
While the study provides a robust analytical foundation, its real value lies in the policy implications it enables. The current trajectory of both lakes suggests that piecemeal interventions—occasional desilting and sporadic clean-up drives—will not reverse degradation. What is needed is a shift towards integrated lake basin management.
The first and most urgent priority is wastewater management. The evidence clearly indicates that untreated sewage is the dominant pollution source, particularly for Salim Ali Lake. Establishing decentralised wastewater treatment systems (DEWATS) within the catchment, coupled with strict enforcement against direct discharge, is non-negotiable. Centralised treatment plants alone are unlikely to suffice in dense urban settings with fragmented drainage networks.
Second, stormwater management must be reimagined. Urban runoff is not merely a hydrological issue; it is a vector for pollutants. Designing separate stormwater and sewage systems, incorporating sediment traps, and restoring natural drainage channels can significantly reduce pollutant loads entering lakes.
Third, catchment-level land-use regulation is critical. The study’s LULC analysis underscores how built-up expansion correlates with declining water quality. Urban planning instruments must integrate hydrological considerations, restricting construction in critical recharge and buffer zones around lakes.
Fourth, nutrient management requires targeted intervention. The presence of orthophosphates and nitrates points to both sewage and agricultural sources. In peri-urban areas, promoting controlled fertiliser use, buffer vegetation strips, and constructed wetlands can reduce nutrient inflow.
Fifth, monitoring systems need to move from periodic to real-time. The study relies on seasonal sampling, which is adequate for research but insufficient for management. Installing sensor-based monitoring systems for key parameters such as turbidity, dissolved oxygen, and conductivity can enable early warning and adaptive response.
Reframing urban lakes as infrastructure
A deeper issue underlying the findings is conceptual. Urban lakes in India are rarely treated as infrastructure. They are seen as aesthetic or ecological assets, not as integral components of urban water systems. This perception limits investment, weakens accountability, and delays intervention.
The study implicitly argues for a paradigm shift. Lakes must be integrated into urban water planning frameworks—linked with wastewater management, flood control, groundwater recharge, and climate resilience strategies. In semi-arid regions like Chhatrapati Sambhajinagar, where rainfall is erratic (~725 mm annually) and drought risk is high, the stakes are even higher.
From a climate adaptation perspective, degraded lakes represent a lost opportunity. Healthy lakes can buffer extreme rainfall events, support base flows, and enhance urban microclimates. Polluted lakes, by contrast, become liabilities—sources of disease, odour, and ecological collapse.
The way forward: From studies to action
The recommendations emerging from the study are not novel, but their urgency is. Awareness campaigns, pollution source identification, and regulatory enforcement have been discussed for decades. What is different now is the convergence of pressures—urbanisation, climate variability, and resource scarcity—that make inaction untenable.
A practical way forward would involve establishing a lake management authority at the city level with clear jurisdiction over both lakes and their catchments. This authority must be empowered to coordinate across departments like urban local bodies, pollution control boards, irrigation agencies, and planning authorities.
Equally important is community engagement. The study notes that local populations continue to use lake water for domestic purposes, despite contamination. This reflects both dependence and a lack of alternatives. Any restoration strategy must therefore integrate livelihood and access considerations, ensuring that improved water quality translates into tangible benefits for communities.
Finally, future research must build on this study’s foundation. Long-term monitoring, integration of biological indicators, and the use of machine learning models for predictive analysis can deepen understanding and improve management outcomes.
A warning for urban India
The story of Salim Ali Lake and Harsul Lake is not unique. Across India, urban lakes are struggling under the combined pressures of population growth, inadequate infrastructure, pollution, and climate stress. This study offers more than a snapshot of declining water quality. It provides a clear illustration of how urban development decisions shape the health of water bodies and, in turn, the wellbeing of communities that depend on them.
The evidence is clear. Without systemic interventions, lake degradation will continue, bringing ecological, public health, and water security consequences. Yet the study also demonstrates the value of science in guiding solutions. The challenge before cities is no longer understanding the problem. It is acting on what is already known. For India's growing cities, protecting lakes is not simply an environmental priority. It is an investment in water security, climate resilience, and urban futures.