There is a river in Asia which has unique hydrological dynamics. The Tonle Sap lake is the largest in Southeast Asia, and the Tonle Sap river is the supplier of water to the lake and a tributary of the Mekong. The river is an inflow in the rainy season, and a outflow in the dry season. The unique hydrology of this river is responsible for the vast biodiversity in this region, and has been listed as a biosphere reserve by UNESCO.