Tonle Sap Lake – One of the World’s Most Productive Freshwater Ecosystems

Caitlin Dempsey


Located in Central Cambodia, Tonle Sap Lake is the largest lake in Cambodia and is considered one of the world’s most productive freshwater ecosystems.   Also known as the Great Lake, Tonle Sap is an ecological hotspot and was named the first UNESCO biosphere in Cambodia in 1997.  

Size of Tonle Sap Lake

The size of Tonle Sap Lake varies greatly, depending on the time of year.  The wet season spans from May to October.  At its height around August or September, monsoonal rains drive enormous amounts of water into the lake from the Mekong River, reversing the flow of the Tonle Sap River northward.  This swells the size of the lake from 2,590 square kilometers during the dry season to about 24,605 square kilometers during the wet season as well as increasing from a depth of only one meter to about nine meters. The dry seasons spans from October to April, during which the flow of the Tonle Sap River returns to flowing towards the ocean.  

Map showing the extent of expansion of Tonle Sap Lake during the wet sea on. Click on map for larger image. Source: UNITAR / UNOSAT.
Map showing the extent of expansion of Tonle Sap Lake during the wet season. Click on map for larger image. Source: UNITAR / UNOSAT.

This cycle has created an ecosystem that supports an incredible high number and abundance of species in the resulting wetlands.    Each year, about 300,000 tons of fish are produced within the ecosystem of the lake which provides about 60% of Cambodia’s protein intake.  

Biodiversity of Tonle Sap

According to a paper by Campbell et al (2006): “At least 149 species of fish are recorded from the lake and it provides habitat for 11 globally threatened and 6 near-threatened species of vertebrates including globally important populations of Spot-billed Pelican, Greater Adjutant, Bengal Florican, Darter, Grey-headed Fish Eagle and Manchurian Reed Warbler.”  The paper also noted that the lake probably supported the world’s largest harvest of freshwater snakes.  Noting the extreme medication of the natural habitat for farming, timber harvesting, and homes, the researchers also noted that over 200 species of higher plants have already been recorded.

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Ecological Impacts to Tonle Sap Lake

Population growth, overfishing, the cutting of mangroves that protect young fish, the building of dams upstream from Tonle Sap Lake, and climate change that has lengthened the hot, dry season are endangering this ecological hotspot.  Researchers are seeking to apply an ecosystem based management tools called the Multiscale Integrated Model of Ecosystem Services (MIMES) to study how different factors affect the health of Tonle Sap and the population that depends on this valuable ecosystem for their livelihood.  Started in 2012, the Tonle Sap research project will take several years to complete.

Further Resources

Campbell, Ian; Colin Poole, Wim Giesen, John Valbo-Jorgensen (2006). “Species diversity and ecology of Tonle Sap Great Lake, Cambodia“. Aquatic Sciences 68: 355–370.

Varis, Olli; Kummu, Matti; Keskinen, M.; Sarkkula, J.; Koponen, J.; Heinonen, U.; Makkonen, K. (2006) “Tonle Sap Lake, Cambodia: Nature’s affluence meets human poverty“.  Human Development Reports, United Nations Development Programme.

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.