Crossing Tonle Sap River by Boat

Tonlé Sap

Tonle Sap River connects Tonle Sap Lake with Mekong River.  

The main reason for the Tonlesap Lake's natural wealth is unique annual phenomena called the "return of the river". This means, the Tonle Sap river, connecting the lake with the Mekong river, regularly changes its direction. Usually it is the outlet of the Tonle Sap lake, but in June it becomes an inflow of water to the lake. The reason is the flood of the Mekong river fed by snow melting in the Himalayas and heavy monsoon rainfalls at the same time. The increasing Mekong water level then reverses the flow of the Tonle Sap river. Thereby the Tonle Sap lake is a natural buffer of the Mekong river system, avoiding too heavy floods in Cambodia's central plains. This return of the river supports the migration of Mekong fish, they come to the lake for spawning. The water level of this extraordinary inland lake raises 7 metres during the annual rainy season, after above-average recipitation even 9 metres.