Catching a glimpse of the Indian Eagle Owl is not a rarity for birders and nature enthusiasts who frequent the Nanmangalam Lake and the surrounding forests. Yet, this privilege is under threat as the lake’s once-thriving ecosystem faces severe environmental degradation.
Fed by rainwater from the hillocks of the Nanmangalam Reserve Forest, the lake — spread over 200 acres — is now ravaged by encroachments, illegal water extraction, sewage and garbage disposal.
Chennai has two significant reserve forests: the Pallikaranai Wetland and the Nanmangalam Scrub Forest. Located along the Tambaram-Velachery Main Road, Nanmangalam Forest is one of the last remaining “lung spaces” in the city.
Spanning approximately 320 hectares, this reserve thrives across hillocks and plains, supporting diverse flora and fauna. It is home to 442 species of flowering plants, 100–125 species of birds, 40 species of butterflies, and nearly 20 species of damselflies and dragonflies. A key attraction in the forest is the Indian Eagle Owl, a scheduled species that breeds exclusively in this area.
In the third part of the series on the deterioration of lakes in the Pallikaranai watershed, we examine the current state of Nanmangalam Lake and the ongoing struggles residents and environmentalists face in their efforts to conserve it. In earlier articles, we focussed on the pollution in Sembakkam and Madambakkam lakes.
Read more: Lessons from the past must guide the restoration of Chennai’s lakes
Impact on biodiversity
The environmental degradation of Nanmangalam Lake and the surrounding Nanmangalam Forest has had a significant impact on local biodiversity. S Mohan, President of the Environment Awareness and Protection Association, points out that the Indian Eagle Owl, which depends on insects from the lake for sustenance, is increasingly threatened due to the disruption of the food chain caused by pollution. “The biodiversity chain is broken, and as a result, the number of exclusive species like the Indian Eagle Owl is declining,” he adds.
Despite the challenges, the lake’s shallow edges continue to attract migratory birds. Species like Temminck’s Stint, Painted Snipe, Common Snipe, and the Western Marsh Harrier are regularly spotted around the lake. Kumaresan Chandrabose, a naturalist based in Chennai, says that the area also serves as a migratory corridor for birds such as the Chestnut-winged Cuckoo and the Korean Flycatcher (a first record for Tamil Nadu), which rely on the ecosystem during migration periods. However, the ongoing construction along the lake’s edges contributes to habitat alteration, potentially disrupting bird populations and leading to shifts in their patterns.
Pollution in inlet channels
The degradation of Nanmangalam Lake began in the early 1960s when large portions of the surrounding scrublands were opened up for limestone mining. This had a catastrophic effect on the region’s ecological balance and biodiversity. The Tamil Nadu Forest Department took control of the area in 1974, and mining has been banned ever since. However, the abandoned limestone quarries that served as a catchment area for the lake still contribute to its pollution.
Mohan explains, “When the limestone is extracted from the mountain, the water flowing from this catchment area becomes polluted with limestone residue.”
While the water from limestone quarries is one of the inlet sources for Nanmangalam Lake, it also receives water from Pachamalai Hills via Chitlapakkam Lake, Selaiyur Lake and Sembakkam Lake. These water bodies, contaminated by sewage from surrounding residential areas, further exacerbate the pollution in Nanmangalam Lake.
The lack of a proper sewage treatment facility in the Nanmangalam residential areas only adds to the problem. “Many apartment complexes do not adhere to the CMDA mandate to install Sewage Treatment Plants (STPs), leading to untreated sewage being dumped directly into the lake,” Mohan adds.
Illegal water extraction from Nanmangalam Lake
Moreover, Nanmangalam and Keelkattalai lakes are at the epicentre of illegal water extraction by private water companies in the suburbs of Chennai.
“The private water companies illegally extract water from large wells a few metres from the lake bund. It is carried through illegal pipelines to makeshift filling stations along the Nanmangalam Main Road. From there, the private tankers take multiple trips in a day,” says V Sivaprakasam, Secretary of the Federation of Welfare Associations, Nanmangalam.
According to Mohan, around 44 private water companies operate around the Nanmangalam Lake.
“We are particularly concerned about the quality of water being supplied by these tankers, as they source their water from the polluted lakebed of Nanmangalam Lake,” notes Sivaprakasam. His fear is valid as there is no mechanism to monitor how these private companies process/treat the water supplied to residents. The presence of faecal coliform bacteria in lakes like Madambakkam sets precedence to Sivaprakasam’s concerns.
If you want to test the water quality in your area, here is an explainer that will help you.
Nanmangalam Lake, the garbage dumping ground
In addition to sewage pollution, Nanmangalam Lake has become a dumping ground for waste. Sanitary workers in the area dispose of garbage near the lake, which the Nanmangalam Panchayat has designated as a transfer point. The situation is made worse by meat shops in the locality, which dispose of their waste directly into the lake.
“Since there is no other space for a transfer point in the locality, we are planning to regulate it by lining a plastic sheet or building a concrete platform to ensure the leachate from the garbage does not get into the Nanmangalam Lake. To prevent illegal garbage dumping on the lake, we are planning to fence the lake, install CCTV cameras and deploy security personnel,” says S Sangeetha, Chairperson of the St Thomas Mount Union (under whom Nanmangalam Panchayat comes).
The indiscriminate dumping of garbage disrupts water flow, leading to the accumulation of plastic waste and threatening local wildlife, particularly birds and fish. “The waste materials release potent chemicals into the water, posing significant health risks to nearby communities and also to the aquatic life,” warns Kumaresan.
Read more: Saving the eri: How communities came together to restore Chennai’s lakes
Flooding in Nanmangalam Lake
Nanmangalam Lake also faces a serious flooding issue. Over the years, the lake has not been desilted or deepened, resulting in a shallow water body that cannot retain excess water. When there is a high inflow of water, it quickly overflows into the exit drain.
However, the exit drain is encroached upon by nearby buildings, which causes the water to overflow into residential areas, leading to frequent floods. Agricultural lands surrounding the lake, which rely on the excess water, are also affected by the blocked exit drain, forcing farmers to depend on groundwater instead.
Sangeetha says that they are pushing for a sewage treatment plant and underground drainage facilities with the concerned departments. “There is also a proposal to restore Nanmangalam Lake and develop it as a tourist spot with boating facilities,” she adds. However, when asked about restoration plans, a Water Resource Department official in charge of the lake, said there were no restoration plans or proposals and refused to comment any further.
Jurisdiction issue and the need for action
Another hurdle is the jurisdictional dispute between the Nanmangalam Panchayat and Sembakkam Corporation. Neither of these bodies has taken responsibility for Nanmangalam Lake’s upkeep, which has affected the allocation of funds.
As part of the lakefront development project, the CMDA has allocated ₹10 crore to Sembakkam Lake, the upstream source for Nanmangalam Lake. However, since treated water flows into Nanmangalam Lake, the investment will be futile unless funds are also allocated to rejuvenate the downstream lake.
Community involvement is important for the sustainable maintenance of local lakes. Residents of Nanmangalam have united to save Nanmangalam Lake, and officials must utilise this momentum to preserve the lake and its biodiversity. We reached out to the WRD officials for their comments on these issues but did not get a response.
You can follow the work of the Saving Nanmangalam Lake group on Facebook.
Demands for Nanmangalam Lake
- Form a separate committee to save the lakes on the outskirts of Chennai
- Arrest sewage inflow
- Desilt and deepen the lake
- Install CCTV cameras to prevent garbage/meat waste dumping
- Initiate a comprehensive study on Nanmangalam Lake with the expertise of government institutes like IIT-Madras or Anna University to assess the lake’s ecological health and suggest solutions
- Use the 1906 survey, which marks the entry and exit points of the lake, as a basis to restore water pathways from Pachamalai Hills to Pallikaranai Marshland
Good and correct article.water body develop tourist spot is not correct madam.
OVER ALL SHOBANA’S COVERAGE OF THE ISSUE IS GOOD. YET, RESPONSIBILITY OF P.W.D. WHICH IS PRIMARILY AND BASICALLY RESPONSIBLE FOR THE MAINTENANCE OF NANMANGALAM LAKE COULD HAVE BEEN HIGHLIGHTED. BEFORE IT IS TOO LATE TO REDEEM THE LAKE, THE WATER SHOULD BE TESTED AND CITY POPULACE SHOULD BE ALERTED. GOOD JOB BY THE CORRESPONDENT.