A group of 22 ecologists, hydrologists, ornithologists, and marine biologists have written to Tamil Nadu Chief Minister M.K. Stalin to stop the Mamallan Reservoir project in the Kovalam-Nemmeli backwater system. They warn it will cause irreversible damage to a critical coastal wetland. In their letter to the Chief Minister and Additional Chief Secretary for Environment, Climate Change and Forests, the scientists pointed out that Tamil Nadu’s own 'Ecosystem Health Card' and the Department of Environment’s studies highlight the importance of tidal flow for brackish wetlands. They said limiting this tidal exchange changes salinity, temperature, and water circulation, harming marine biodiversity. The group explained that Kovalam-Nemmeli backwaters are a tidal-marsh ecotone linked to the Bay of Bengal through inlets at Kovalam and Kokilimedu. The southern stretch near Mamallapuram is still healthy due to active tides, but the Nemmeli stretch is already showing signs of damage due to roads and bunds. These wetlands support seagrass patches, mudflats for migratory birds, and brackish habitats essential for juvenile fish and shrimp. Turning this area into a freshwater reservoir would destroy these ecosystems, threatening fisheries, bird habitats, and natural coastal protection. The scientists also raised concerns about flood risks. The project's Environmental Impact Assessment says flooding in nearby villages is due to drainage blockages on Old Mahabalipuram Road and Kelambakkam-Kovalam Link Road. However, the reservoir plan does not fix these issues. Building 4.5-metre bunds inside this tidal floodplain might remove natural flood buffers and increase risks during cyclones. They urged the government to declare the site a protected lagoonal wetland. This move, they said, would promote biodiversity, protect fisheries, and strengthen climate resilience. Notable signatories include Asad Rahmani, former Director of Bombay Natural History Society; John Kurien, former Professor at Centre for Development Studies; Romulus Whitaker of Madras Crocodile Bank; D. Narasimhan of Madras Christian College; Ravi Chellam, wildlife biologist; environmentalist Ashish Kothari; Lalitha Kamath of TISS; Matthew Gandy from University of Cambridge; Nikhil Anand from University of Pennsylvania; and others.