Sasathamcotta Lake or Sasathamkotta 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.