Tonle Sap is Cambodia’s largest freshwater lake and the largest freshwater lake in Southeast Asia, with Irrawaddy dolphins associated with its wider Mekong-connected ecosystem.
The lake’s name means “Great Lake” in Khmer. Its remarkable seasonal pulse reverses the flow of the Tonle Sap River: monsoon water from the Mekong expands the lake dramatically, flooding surrounding forests and creating vital fish habitat.
Tonle Sap supports one of the world’s most productive inland fisheries and was designated a UNESCO Biosphere Reserve in 1997. Its floodplain also shelters fish-eating birds, reptiles, and other wildlife.
A common mix-up is confusing Tonle Sap with the Mekong River. The Mekong supplies much of the lake’s seasonal water, but Tonle Sap is the lake itself. The lake is also sometimes called the Great Lake of Cambodia.