Sasthamkotta Lake is the largest freshwater lake in Kerala. The lake is located at Sasthamkotta in Kollam District. It is located at a distance of thirty kilometers from Kollam. The lake supplies water to the entire Kollam district.

The lake is encircled by hills on three sides and in the south of the lake there is a bund, which has been constructed to separate the lake from the adjacent rice fields. The Sastha Temple is situated on the banks of the Sathamkotta Lake. In November 2002, the lake was notified as a wetland of international importance under the Ramsar Convention.