Scientists urge T.N. CM Stalin to withdraw Mamallan Reservoir proposal

Scientists urge Tamil Nadu's CM to withdraw the Mamallan Reservoir proposal, citing severe risks to coastal wetland ecosystems.

A group of 22 ecologists, hydrologists, ornithologists, and marine biologists have written to Chief Minister M.K. Stalin, urging the Tamil Nadu government to withdraw the proposed Mamallan Reservoir project in the Kovalam-Nemmeli backwater system, warning that it would irreversibly damage a critical coastal wetland.

In a letter addressed to the Chief Minister and the Additional Chief Secretary for Environment, Climate Change and Forests, the signatories said Tamil Nadu’s own ‘Ecosystem Health Card’ for wetlands in the State and the Department of Environment’s publication on lagoon ecosystems show that brackish wetlands depend on tidal exchange. Restricting tidal flow, they noted, alters salinity, temperature, and circulation, limiting marine biodiversity.

They argued that the Kovalam-Nemmeli backwaters are a tidal-marsh ecotone connected to the Bay of Bengal through the Kovalam and Kokilimedu inlets, not an inland freshwater depression. While the southern stretch near Mamallapuram remains ecologically functional due to continued tidal inflow, the Nemmeli stretch — already fragmented by roads and bunds — shows early signs of degradation.

The wetland, they said, supports seagrass patches, mudflats used by migratory waders, and brackish habitats essential for juvenile fish and shrimp. Converting it into a freshwater reservoir would destroy these functions and undermine fisheries, bird habitats and natural coastal protection.

The group also flagged hydrological risks, stating that the project’s Environmental Impact Assessment attributes flooding in western villages to drainage bottlenecks along the Old Mahabalipuram Road and the Kelambakkam-Kovalam Link Road. The proposed reservoir does not address these choke points, they said, and constructing 4.5-metre bunds within a tidal floodplain could remove natural flood buffers and increase cyclone-related risks.

Urging the government to declare the site a protected lagoonal wetland instead, the scientists said such a move would strengthen biodiversity conservation, fisheries, and climate resilience.