Tonlé Sap Biosphere Reserve

Tonle Sap, Siem Reap, Cambodia

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The Tonlé Sap Biosphere Reserve in Cambodia surrounds Tonlé Sap Lake, Southeast Asia’s largest freshwater lake, which dramatically expands in size during the rainy season due to a unique reverse flow from the Mekong River.

This seasonal flooding creates a vast wetland ecosystem of lakes, floodplains, and forests that supports an extraordinary biodiversity of over 200 plant species, around 225 bird species—including endangered ones—and a wide range of mammals, reptiles, and fish. The lake is vital for Cambodia's inland fisheries, providing more than half of the country’s freshwater fish catch and sustaining the livelihoods of about 3 million people.

Established as a UNESCO Biosphere Reserve in 1997 and officially designated in 2001, the area balances conservation with sustainable development, education, and research. The floating forests act as natural flood barriers and breeding grounds, but challenges like illegal fishing, habitat loss, and poverty near the lake threaten its delicate ecological and social balance.