Vembanad Lake is the longest lake in India and the largest lake in the state of Kerala. It is part of an extensive wetland system with the largest source of surface water. A number of rivers flow into the lake making it deep and vast. The lake is divided into 2 halves by a saltwater barrier and you can see the difference between the brackish and fresh water. It was constucted to prevent intrusion of sea water. The serene lake comes alive during Onam with a spectacular water regatta - the snake boat races. It is indeed amazing to watch oarsmen, at least a hundred in one boat, slice their way through the waters to the fast rhythm of their own full throated singing. Vembanad Lake is at the heart of Kerala Backwaters tourism with hundreds of kettuvallams plied on it and numerous resorts on its banks. The Kumarakom Bird Sanctuary is located on the east coast of the lake. The lake has become a major tourist attraction.