Sasthamcotta Lake or Sasthamkotta Lake, also categorized as a wetland, is the largest fresh water lake in Kerala, a state of India on the south of the West Coast.
The lake is named after the ancient Sastha temple (a pilgrimage centre) located on its bank. It meets the drinking water needs of half million people of the Quilon district
and also provides fishing resources. The purity of the lake water for drinking use is attributed to the presence of large population of larva called cavaborus that consumes bacteria in the lake water. The lake is a designated wetland of international importance under the Ramsar Convention since November 2002.
The lake is located at a distance of 25 km from Quilon city, which is on the northern side of Ashtamudi Lake. Thiruvananthapuram International Airport, at 105 km,
is the nearest airport to Kollam. Karunagapally, at a distance of 8 km, is the closest town to the lake. A ferry service across the lake transports people between West Kallada
and Sasthamkotta. Except for an earthen embankment of 1.5 km length which separates the lake from the paddy fields on its southern side, bordering the alluvial plains of the Kallada River, all other sides of the lake are surrounded by hills which are steep and form narrow valleys. In the south and southwestern parts of the lake there are a number of smaller water bodies and waterlogged areas.The present area of the lake is 375 ha since large part of the lake is reported to have been occupied for agriculture. Rock formation of mainly archaean origin are recorded with intrusions of charnockite, biotite gneiss and dolerite dyke rocks. The Tertiary Varkala formations are observed along the coastal beds. In the valley portion, sand and silt deposits are recorded. Geomorphological divisions of the basin area of the lake comprise a) the undulating uplands which have fairly thick vegetation of mixed crops and plantations, b) the valley fills of laterite alluvium and colluvial deposits with low level areas which are intensely cultivated and thickly populated and c) the flood plains/alluvial plains of the Kallada River on the south that are mostly cultivated.
