The fish biodiversity of the Tonle Sap Lake is depending on the annual flooting cycles, reaching the lake from the Mekong River via the Tonle Sap River. 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 River.
Seasons of the Tonle Sap Lake
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 16,000 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 2,500 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.
Lake Tonle Sap with the rivers Mekong, Tonle Sap and Bassac form a unique eco-system, home to a great variety of 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.
Overfishing, untreated industrial and domestic sewage, climate change effects, and dam building projects along the inflows threaten the natural balance of the region.
In 1997, Tonle Sap was nominated as a UNESCO biosphere reserve (TSBR) encompassing the whole lake. Additionally in 2001, the Tonle Sap Biosphere Reserve was issued by the government of Cambodia by royal decree.