Lake · Cambodia
Tonlé Sap
Tonlé Sap in Cambodia is the largest freshwater lake in Southeast Asia. In the rainy season it grows to several times its size, and a river even changes direction to fill it up.
Picture credit: Jakub Hałun (CC BY-SA 4.0) · HansenHimself (CC BY 4.0) · Anandajoti (CC BY-SA 3.0) · Wikimedia Commons
Where is Tonlé Sap?
Countries on its shores: Cambodia.
Largest lake of: Cambodia.
Middle of the lake: 12.88° N, 104.07° E
The story behind it
In the dry season, Tonlé Sap is a wide, shallow lake of about 2 700 km², often only a few metres deep. Then the rainy season comes and the great Mekong River rises. Its water pushes into the Tonlé Sap River, and this river turns around and flows backwards into the lake! The lake then grows to more than 10 000 km² and becomes up to about 14 m deep, so its size changes a lot during the year. Well over 140 kinds of fish live here, among them the huge Mekong giant catfish. About 1.2 million people depend on the lake, and some of them live in floating villages. When the river flows back towards the Mekong, Cambodians celebrate the Water Festival with big boat races. Tonlé Sap is also the largest lake in Cambodia. Long ago it helped to feed Angkor, a huge ancient city.
Find it on the globe
Tonlé Sap is there as a small blue dot with its name, right on the water. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.
It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.
Questions children ask
How big is Tonlé Sap?
In the dry season Tonlé Sap covers about 2 700 km². In the rainy season it grows to more than 10 000 km², so its size changes a lot.
Why does the Tonlé Sap River flow backwards?
In the rainy season the Mekong rises so high that its water pushes into the Tonlé Sap River and makes it flow into the lake. For about six months of the year it flows one way, and for six months the other way.
Is Tonlé Sap the largest lake in Cambodia?
Yes. Tonlé Sap is the largest lake in Cambodia and even the largest freshwater lake in all of Southeast Asia.
Where these numbers come from
Every figure on this page was checked against public reference sources before publication. Where sources genuinely disagree, the text says so.
Last checked: