Bengaluru is known as a city of lakes. Where once there were more than a thousand lakes, we now have under three hundred lakes, which is still unique when compared to other cities in India. These lakes played a large role in flood mitigation, as water sources and as ground water recharge sinks. Increasingly those roles have come under stress due to the rapid urbanisation and concretising of the city.

The lakes in Bengaluru are part of an interconnected stream system, and fall under three major valleys – the Koramangala-Challaghatta valley and the Yelahanka valley systems which drain into the Ponnaiyar river, and the Vrishabhavathi valley system which drains into the Arkavathi, which itself is a tributary of the Kaveri.

What is the state of these lakes in Bengaluru today? How has the urbanization and growth in population of the surroundings affected them? What role can these lakes play today in these circumstances, in terms of flood mitigation and groundwater recharge? How robust or active are the old stream networks in this day? These are some of the questions that the participants of the “Bengaluru Lakes” datajam sought to answer for the different lake systems of the city.

Bengaluru Lakes Datajam

The datajam was conducted in partnership with Biome Environment Trust, Friends of Lakes, Paani.Earth and WELL Labs, and supported by venue partner Samagata Foundation. The event was conducted in Samagata Foundation’s space at the 4th Floor, “Cobalt”, Church Street, Bengaluru – 560001.

In the day long event, 35 participants from diverse backgrounds – lake volunteers with experience working with lakes and authorities, GIS experts, developers, urban planners, activists and citizens came together to analyse data on lakes in Bengaluru. The outputs were informed by lake audits conducted by different lake groups in different lake systems in the city over the past week.

Lake Systems

Unlike in earlier datajams, the lake systems were chosen based on presence of lake volunteers in the lake audit and interest from people in different parts of the city. Once chosen, the task of the participants was to come up with a state of the lakes report, to look at the historic and cultural context of the lakes, current status in terms of pollution and flooding, changes to the lakes over the decades and improvements needed in addressing the issues seen.

Based on the lake audits, the following lake systems were chosen during the datajam:

1. North – Yelahanka Lake System comprising Attur, Puttenahalli, Yelahanka and Rachenahalli lakes.
2. South – Thalaghattapura, Jogikere, Sompura, Lingadhiranahalli and Vajarahalli kunte lakes.
3. West – Srigandhadakaval, Herohalli and Mallathahalli lakes.
4. South East 1 – Chikkabellandur, Otikere, Gunjur Palya and Carmelaram lakes.
5. South East 2 – Soul Kere, Kaikondarahalli, Kasavanahalli and Parappana Agrahara lakes.

Outputs

North – Yelahanka Cascade

Team comprising Aditya, Akash, Chandrashekar, Diwakar, Malkan, Ramprasad, Ramya, Sachin, Sindhu and Sukanya looked at the Yelahanka lake system. For the purpose of the datajam they concentrated on three lakes – Yelahanka, Attur and Puttenahalli.

They noted the loss of vegetation around the lakes in the last 12 years, and increase in encroachment on lake boundaries. Rapid urbanization around the lakes has also led to flow of sewage into the lakes with the result that biodiversity as seen from citizen science portals like ebird has taken a hit even in important habitats like Puttenahalli.

They found that sewage channels have been blocked by overgrowth and sewage was seen flowing even on the walking paths around the lake. The team computed the cost of the encroached land and found that such land was worth upwards of Rs. 6000 crores making it lucrative to encroach on lakes and rajakaluves. Given these circumstances they wondered how easy it would be to solve the problem of encroachment on lakes.

South – Thalaghattapura Lake System

Ajit Singh, Chaithanya, Parikshit, Saurabh, Subrahmanya and Uma looked at the lake systems of South Bengaluru around Kanakapura Road. These lakes include Thalaghattapura Lake, Jogi Kere, Sompura lake, Vajarahalli Kunte among others. While Sompura and Lingadheeranahalli lakes drain into the Vrishabhavathi river, the other set of lakes – Thalaghattapura Lake, Jogi kere and Vajarahalli (Byyanakunte) lake – drains into the Suvarnamukhi river, which is a tributary of the Vrishabhavathi.

They noted the alarming flow of sewage into the lakes, reduction in the catchment areas, and lack of maintenance of inlet and outlet drains of the lakes. The flow of sewage has also led to a water hyacinth infestation in the water body. Thalaghattapura lake was recently rejuvenated by BBMP and issues like dumping of waste and open defecation by the lake bed have been addressed since then. The lake teams also observed new encroachments at Vajarahalli lake during their visit.

West – Srigandhadakaval and Herohalli Lakes

Team comprsing Ellen, Parimel, Shobha Bhat, Sharath, Sonesh and Vaibhav looked at the lake system originating in Herohalli and flowing past Srigandhadakaval and Mallathahalli lakes to end up in the Vrishabhavathi river. They found significant differences between the geographical drainage flow and the drainage network of BBMP connecting the lakes.

Unlike other lakes in the city, sewage isn’t an issue with these lakes, which also dry up during summer. However, they face encroachment within the lake body by BBMP itself for various infrastructure like play areas, gyms, walking paths and concrete fencing. Garbage dumping was an issue which got resolved after multiple requests to the authorities.

South East 1 – Carmelaram lake

Team comprising Chetan Gopal, Gaurav, Shachi Pathak, Shwetha, Utkarsh and Vivek analysed the status of the set of lakes comprising Chikkabellandur, Gunjurpalya and Carmelaram lakes. These lakes are part of the Koramangala-Challaghatta valley and drain into Varthur lake before draining into the Ponnaiyar river in Tamil Nadu.

During the datajam they analysed the state of Carmelaram lake. They noted that the lake is small, with an area of 8 acres and was a wasteland until it was rejuvenated in 2024 by BBMP. However, the outlet weir is still under construction and while it should reach Gunjur Palya lake, it is missing in most parts.

The lank bund is however allowing tractors to enter a private land at one corner of the lake and dump unsegregated solid waste there. This could pose a problem to the lake going forward. The restoration itself seems to have improved the water levels in the surroundings with borewells of 300-400ft coming alive with the rains of 2024. They noted that BBMP has spent around Rs. 13 Lakh on maintenance of three lakes – Chikkabellandur, Carmelaram and Gunjur Palya but the work order details don’t give a lake-level split-up.

South East 2 – Sowl Kere, Kaikondarahalli, Kasavanahalli and Parappana Agrahara lakes

Team comprising Ayush, Rashmi, Rajalakshmi, Shalini, Spandana, Thiyaku and Valli analyzed another lake system in South East Bengaluru comprising of Sowl Kere, Kasavanahalli, Kaikondarahalli and Parappana Agrahara lakes. This lake system originates in the Parappana Agrahara lake and flows towards Sowl Kere before flowing to Varthur Lake on the way to the Ponnaiyar river.

They noted issues like parts of the lake being marked as private property in the case of Sowl Kere, untreated sewage flowing into the lakes, rejuvenation which ends up making soup bowls out of thriving wetlands, and rampant encroachments on the lake buffer zones. The diversion channels were also found to have less capacity leading to repeated flooding instances in the area.

They recommended that citizen groups be involved in the maintenance and upkeep of lakes, buffer zone encroachments be cleared, the underground drainage and STP projects in the area be completed soon, and additional channels be created to help clear storm water to help mitigate flooding.

Conclusions

All teams noted regular encroachment on either the lake areas or on the stream/storm-water drain network connecting the lakes. Concretisation of surroundings was also seen to be contributing to the lakes not working as well as they could for flood mitigation. In the case of Carmelaram lake, the rejuvenation was seen to have helped ground water recharge, so this was a story that BBMP needs to build on.

In many cases the drains network connecting the lakes was either seen broken or in bad shape. In some cases they were forced to work with the built up environment needing to take right angle turns which would affect the carrying capacity of the drains, especially during heavy rains.

Except in the west, flow of drainage into the water body was a persistent issue faced by all the lakes, either directly or indirectly because of upstream lakes. This had led to issues like fish kill, growth of water hyacinth, loss of biodiversity among other issues. In the case of Puttenahalli lake in North Bengaluru the walking path was seen submerged entirely by sewage. Where there are STPs, they were seen to not have the capacity to deal with the inflow. Most recommendations for lakes wanted this issue to be tackled at high priority.