Ousteri Lake, also known as Osudu Lake or Lake Ousteri, is a large freshwater lake located in the Union Territory of Puducherry (formerly Pondicherry), India. It is situated approximately 10 kilometers from the city center of Pondicherry.

Ousteri Lake is one of the largest and most important wetlands in the region. It spans an area of around 390 hectares, making it a significant ecological hotspot. The lake serves as a catchment area for several small rivers and channels, contributing to the groundwater recharge in the surrounding region.

The lake is not only a picturesque natural attraction but also plays a vital role in maintaining the local ecosystem. It supports a diverse range of flora and fauna, including numerous species of resident and migratory birds. The lake and its surrounding wetlands are a designated bird sanctuary, making it a popular destination for birdwatching enthusiasts.