The story so far: The proposed Mamallan Reservoir in Chengalpattu district is being presented as a solution to two problems facing the rapidly urbanising southern parts of the Chennai Metropolitan Area — drinking water shortage and flooding. But the project is also being built in a landscape of marshes, salt pans, backwaters, and wetlands that supports fishing and provides feeding and roosting habitat for birds. This has raised concerns among fishing communities, residents, and environmental groups over its potential impact on wetlands, fisheries, and local hydrology.

The reservoir has been proposed by the Water Resources Department (WRD) in the Kovalam sub-basin between the Old Mahabalipuram Road (OMR) and East Coast Road (ECR), stretching across parts of Thiruporur and Thirukalukundram taluks. The project received Coastal Regulation Zone (CRZ) clearance, and construction formally began in January 2026 during the erstwhile DMK regime. The incumbent TVK-led coalition government is also backing the project.