Tônlé Sap River

The Tônlé Sap is a shallow lake in western Cambodia which is part of the Mekong River system. It is the largest lake of Southeast Asia and is fed by numerous streams. During the dry season it drains by the Tônlé Sap River southeast to the Mekong River. During the wet monsoon season of June to November, the high waters of the Mekong River reverse the flow of the Tônlé Sab River and increase the size of the lake from 2,600 to 10,400 sq km (about 1,000 to 4,020 sq mi). When the high waters of the Mekong River recede, the flow reverses. This natural mechanism provides a unique and important balance to the Mekong River down stream of the lake and ensures a flow of fresh water during the dry season into the Mekong delta in Vietnam which buffers the intrusion of salt water from the South China Sea into the rich agricultural lands of the delta.