Tonle Sap, Cambodia

Tonle Sap floodplain, Cambodia Photo
Nearly 77,000 acres of critical habitat located near Tonle Sap lake are now protected areas for Sarus cranes, storks, ibises, and other rare waterbirds native to the area.
©Eleanor Briggs

The largest lake in Southeast Asia, the Tonle Sap supports huge colonies of waterbirds—storks, ibises, pelicans—and more than a million people who rely on fish from the lake for protein and livelihoods. The Tonle Sap River is unusual because its flow changes direction twice a year. During Cambodia's dry season, from November to May, it drains into the Mekong River at the capital, Phnom Penh. In June, the monsoon season's heavy rains begin, and the Tonle Sap River reverses direction and flows into the Tonle Sap lake. With its large floodplain, rich biodiversity, and high annual sediment and nutrient deposits from the Mekong, the Tonle Sap is one of the most productive inland fisheries in the world.

Fast Facts

  • The most important waterbird colony in Cambodia lies inside the Prek Toal Core Area in the Tonle Sap Biosphere Reserve. This is a critical breeding site for several globally threatened species of storks, ibises, and cranes.
  • The Tonle Sap Biosphere Reserve is some 200 miles southeast of Tmatboey, another major nesting site for rare waterbirds in Northern Cambodia.
  • In the dry season, the Tonle Sap lake has a surface area of around 965 square miles. This increases to between 3,800 and 6,100 square miles in the flood season. 
  • Approximately 1.1 million people live in the area immediately surrounding the lake. The average income is less than 50 cents a day, making it one of the poorest regions of Cambodia.


Overfishing, illegal collection of waterbird eggs and chicks, deforestation, overpopulation, and damming of the Mekong upstream threaten the area and its wildlife.

WCS Responds

WCS and the Ministry of Environment of the Royal Government of Cambodia created a novel approach to protecting the Tonle Sap waterbird colonies from overharvesting. We trained former hunters and egg collectors to become park rangers and monitor the breeding bird colonies around the clock. This project has resulted in the recovery of bird numbers and provided much-needed income for these families.

From the Newsroom

Cambodia Protects Key GrasslandsMarch 18, 2010

Nearly 77,000 acres of critical habitat located near the country’s famed Tonle Sap lake are now protected areas for Sarus cranes, storks, ibises, eagles, and the rare Bengal florican.

The Birds Are BackApril 7, 2008

A single team of park rangers, working round the clock, has helped populations of storks, pelicans, ibises, and other rare waterbirds recover in Cambodia’s famed wetland.

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