The Tonle Sap Lake is the largest freshwater lake in South East Asia and one of the most productive inland fisheries in the world. The lake is connected to the Mekong River through the 100 km long Tonle Sap channel.
During the rainy season from mid-May to beginning October, the water level of the Mekong River is four times higher than in the dry months. Large water quantities flow via the Tonle Sap River in the Tonle Sap Lake, the surface of which can reach up to 10,000 sq. km. Its maximum depth then is about 14 m. In November, when the Mekong River carries less water, the flow direction of the Tonle Sap River changes. Then huge quantities of water flow back from Tonle Sap Lake to the Mekong River, and the surface of the lake shrinks to 3,000 sq. km, its maximum depth amounts to 2 - 3 m only.
Due to this unique natural phenomenum Tonle Sap Lake is very rich in freshwater fish. In the floodplains rice has been cultivated for centuries.
Tonle Sap Lake and its environs are rich in species: over 200 fish species live in the lake, 70 of it are of commercial relevance. 23 snake species, among them the endemic Longhead Water Snake (Enhydris longicauda) as well as 13 turtle species live in and around Tonle Sap Lake.
Lake Tonle Sap with the rivers Mekong, Tonle Sap and Bassac form a unique eco-system, home to a great variety of species. Overfishing, untreated industrial sewage and dam building projects threaten the natural balance of the region.
In 1997, Tonle Sap was nominated as a UNESCO biosphere reserve (TSBR) encompassing the whole lake.
