Ousteri Lake

Ousteri Lake, also called Ossudu Lake after the village of Ossudu, spreads over about 800 hectares across the boundary of Puducherry and Tamil Nadu, with 390 hectares on the Puducherry side, and is Puducherry's largest lake. It is man-made, part of the cascading network of rain-fed tanks that has watered farming in the region for centuries.

Migratory birds use the lake all year, and it is listed as an Important Bird Area and counted among the significant wetlands of Asia. The Puducherry side was declared the Oussudu Bird Sanctuary in 2008 and the Tamil Nadu side in 2015. The lake is a popular tourist spot, with a small boat club run by the Puducherry Tourism Department, and there are plans to make it a national park and to install telescopes for watching birds. Research by the French Institute of Pondicherry has traced its change from a farmers' irrigation tank to a place managed mainly for conservation and recreation.