Bengaluru’s ‘thousand lakes’ legacy faces water quality crisis

In a city once celebrated as the “land of a thousand lakes”, even the last remaining lakes are struggling to breathe.

Between April and November 2025, nearly four in ten monitored lakes in Bengaluru fell into Class E, the poorest water quality category, every single month, according to official Monitoring of Indian National Aquatic Resources (MINARS) data. In all, samples were collected from 149 lakes.

The average condition of lakes across the eight months was 59.5 per cent (Class D) and 40.5 per cent (Class E). The worst month was May 2025, when 46.6 per cent of tested lakes fell into Class E. Not one sampled lake reached Class A, B or C standards, which are categories fit for drinking water (with treatment), bathing or conventional potable supply.

Among the lakes, Vengaihnakere in Mahadevapura, Kannur Lake on Hennur Road, and Rayasandra Tank in Sarjapura are in the worst condition. These indicate continuous sewage inflow. Yelamallapa Chetty, Chikkagubbi, Madiwala, Varthur, Munekolalu, Bandematta, Hosakerehalli and Machohalli are no better. What’s more, lakes such as Ulsoor, Jakkur and Yelahanka are also no better despite generous funding.

For perspective, fecal coliform content is as high as 1.40 lakh MPN/100 ml in Hosakerehalli Lake. That is 280 times higher than the Central Pollution Control Board’s bathing standard (500). In comparison, Sankey Tank fares better (225 MPN/100 ml found) and Kengeri Lake, at 43 MPN/100 ml, ranks among the best.

The MINARS data, published on the official website of the Karnataka State Pollution Control Board, indicates that rainfall provided only temporary relief, while core pollution sources, be it domestic sewage or industrial effluents, remain unaddressed.

In Bengaluru, the responsibility of supplying Cauvery water and managing domestic sewage rests with the Bangalore Water Supply and Sewerage Board (BWSSB), while the five newly carved municipal corporations are in charge of the lakes and all types of stormwater drains (SWDs).

Paradox of investment

The persistence of poor water quality comes despite a decade of heavy capital spending on the construction of large-scale sewage treatment plants (STPs), rejuvenation of lakes, remodelling of SWDs and construction of sewage diversion channels in lakes. Yet, all the waterbodies in Bengaluru have fecal coliform content several times higher than the prescribed standards.

The highest concentration of poor-performing lakes was observed in the city’s outskirts, especially Mahadevapura. Several lakes in this region fluctuated between Class D and Class E, suggesting chronic sewage inflow.

Kochur Shankar, a resident of Horamavu, said a large part of KR Puram has Cauvery and sanitary lines, but houses continue to use septic tanks because the BWSSB is yet to start linking individual houses. “This is because the STP in Kalkere is too small to handle the load. The BWSSB is upgrading the capacity of the existing plant. Until that happens, a lot of sewage will flow into the drains and lakes,” he said.

Going by the number of STPs working and proposed, lakes in Bengaluru should be sewage-free by 2029. Ramprasath Manohar, chairman of the BWSSB, said STPs currently treat about 1,348 million litres of sewage. “In the next two months, the infrastructure capacity for treating sewage will go up by 628 MLD. On top of that, we have proposed an additional nine STPs capable of treating 535 MLD of sewage,” he said, adding that the BWSSB has started releasing treated water into 23 lakes. “We will add 40 more lakes. By doing this, we also plan to promote transparency in the functioning of STPs,” he added.

There is, however, a belief among experts that too much thrust is given to STPs, while coverage of the sanitary network across all streets and establishments should have been the priority.

MN Thippeswamy, a retired BWSSB engineer, said Bengaluru is among the few cities to have a large number of STPs, but the end result has not been promising. “Before Cauvery Stage 5 was commissioned, BWSSB was supplying 1,440 MLD of water. Considering about 500 MLD of groundwater usage and accounting for 80 per cent of total water use as sewage, Bengaluru had plants capable of treating up to 80 per cent of sewage, but no lake was free from sewage at that time,” he said. This, he added, shows that the city does not have a complete network of conveyance systems covering the source of sewage to the plant.

As a temporary measure, the authorities have initiated projects such as sewage diversion channels and bioremediation of lakes, while the critical requirement of detecting the source of sewage discharge and bringing it under the sanitary network remains ignored.

V Ramprasad, convener of Friends of Lake, a collective of citizen volunteers, said no government agency, neither the BWSSB nor the Greater Bengaluru Authority, has set a benchmark for all lakes and strived to achieve that goal. “What’s more concerning is that the BWSSB, which is the primary polluter of lakes in Bengaluru, is part of the Board of KSPCB, which is a regulator,” he said.