Tonle Sap overview

The remarkable Tonle Sap is a river that becomes a freshwater lake in the centre of Cambodia, the largest in Southeast Asia, and then flows down to join the Mekong River just past Phnom Penh. During the dry season, the river feeds the lake and continues to flow downriver. When the monsoon breaks in June, the flow reverses as the Mekong floods and forces enormous quantities of water uphill into the lake, swelling it to five times its size and thus acting as a gigantic natural reservoir. This unique natural phenomenon reduces the force of the torrent rushing towards the sea, and is a major factor in the steady expansion of the Mekong Delta. Fish spawn in the newly flushed lake, covering a seventh of the country at its peak. As the waters recede, the lake teems with fish, some of which have evolved to flop across land to follow the disappearing water. The highly fertile mud left behind is excellent for rice. A unique strain of rice has been developed to suit the conditions – it grows in the rising water reaching a stem length of several metres. The lake, now a National Park, is a key element in Cambodia's economy. Approximately two-thirds of the protein consumed in Cambodia comes from fish from Tonle Sap.