Tonlé Sap (/ˈtɒnl sæp/; Khmer: ទន្លេសាប, Tônlé Sab [tɔnleː saːp]; lit.'Fresh River' or commonly translated as 'Great Lake' is a lake in the northwest of Cambodia. Belonging to the Mekong River system, Tonlé Sap is the largest freshwater lake in Southeast Asia and one of the most diverse and productive ecosystems in the world.[1] It has been designated as a Biosphere Reserve by UNESCO in 1997 due to its high biodiversity.[2] In the 21st century, the lake and its surrounding ecosystems are under increasing pressure from deforestation, infrastructure development and climate change.[3][4][5]

Tonlé Sap
Location of Tonlé Sap in Cambodia.
Location of Tonlé Sap in Cambodia.
Tonlé Sap
Location of Tonlé Sap in Cambodia.
Location of Tonlé Sap in Cambodia.
Tonlé Sap
LocationLower Mekong Basin
Coordinates12°53′N 104°04′E / 12.883°N 104.067°E / 12.883; 104.067
Primary inflowsTonlé Sap River, Siem Reap River, Pursat River, Sangke River
Primary outflowsTonlé Sap River
Basin countriesCambodia
Max. length250 km (160 mi) (maximum)
Max. width100 km (62 mi)(maximum)
Surface area2,700 km2 (1,000 sq mi) (minimum)
16,000 km2 (6,200 sq mi) (maximum)
Average depth1 m (3.3 ft) (minimum)
Max. depth10 m (33 ft)
Water volume80 km3 (19 cu mi) (maximum)
Surface elevation0.5 m (1 ft 8 in)
SettlementsSiem Reap, Battambang


Scenery of Tonle Sap

Tonlé Sap Lake is located in the northwest of the lower Mekong plain, formed by the collision and collapse of the Indian Plate and the Eurasian Plate.[6] The lower Mekong plain used to be a bay, and the sea level rose rapidly at the end of the last glacial period. About 4.5 metres (15 ft) high, cores from this period found near Angkor contain tidal deposits, as well as salt marshes and mangrove swamp deposits,[7] deposited in caves about 7,900-7,300 years ago The sediments of Lake Sap also show signs of marine influence.[8] The current river morphology of the Mekong Delta was developed over the past 6,000 years,[9] while the remaining waters in the northwest corner of the lower Mekong plain formed the Tonlé Sap.[10]



The Tonlé Sap drainage basin is bordered to the southwest by the Cardamom Mountains, with heights of more than 1,700 metres (5,600 ft), and to the north are the Piandan Mountains with an average height of 500 metres (1,600 ft). The basin covers an area of 86,000 square kilometres (33,000 sq mi). The 120 kilometres (75 mi)-long Tonlé Sap River connects the Tonlé Sap Lake with the Mekong River and contributes 9% of the flow of the Mekong River.[5][11] The size and water volume of the lake varies greatly throughout the year, with a minimum area of about 2,500–3,000 square kilometres (970–1,160 sq mi) and a volume of about 1 cubic kilometre (0.24 cu mi) in the dry season,[12] and the water body expands in the rainy season, increasing the depth to 9–14 metres (30–46 ft).[13] The maximum area is 16,000 square kilometres (6,200 sq mi), and the volume is about 80 cubic kilometres (19 cu mi).[12]

About 34% of the water in the Tonlé Sap comes from the rivers that enter the lake, about 53.5% from the Mekong River, and 12.5% from precipitation.[5] May to October is the rainy season in the lower Mekong plain, and November to March is the dry season. The annual rainfall is 1,000 to 4,000 millimetres (39 to 157 in). Almost all the precipitation is in the rainy season.[14] At the end of the dry season, the Tonlé Sap Lake has a typical depth of 1 metre (3.3 ft). As the monsoon rain begins, the water level of the river begins to rise, eventually reversing the flow of the river. The water level of the Tonlé Sap increases by about 10 metres (33 ft), the flow of the Mekong gradually decreases at the end of the rainy season, and the flow of the Tonlé Sap then reverses and begins to replenish the flow of the Mekong.[15]

The extreme hydrodynamic complexity of the Tonlé Sap Lake, both in time and space, makes it impossible to measure specific flow, and water level rather than velocity and volume determines the movement of water as it shapes the landscape.[12] 72% of the modern sediments deposited in the Tonlé Sap come from the Mekong River, while only 28% come from the catchments upstream of the lake.[10] Sediment-bound phosphorus acts as the basis of the food chain through phytoplankton, and internal nutrient cycling plays a crucial role in the productivity of the floodplain and, therefore, the long-term sustainability of the lake's entire ecosystem.[16]


Tonle Sap's flood forests

The land cover of the Tonlé Sap Lake Basin is 55% of the forest land and 45% of the agricultural land.[5] The lake is surrounded by freshwater mangroves known as "flood forests",[17] accounting for 3% of the basin area,[5] and the floodplain is surrounded by low hills and covered with evergreen or deciduous seasonal tropical plants. The forest is dominated by Dipterocarpaceae, Leguminosae, Lacelandaceae, and in some places Pinaceae, Rohan pineaceae or bamboo. As the distance from the lake becomes farther and farther away, the forest gradually turns into a thicket, and finally into a meadow.[17][18] In areas with higher quality soils or higher altitudes, deciduous mixed forests and semi-evergreen forests occur.[19][20] This diversity of vegetation types underlies the species diversity of the Tonle Sap ecosystem, with interlocking forests, grasslands and swamps providing refuge for local wildlife.[20]

The lake is home to at least 149 species of fish, 11 of which are globally endangered, and the lake area is also home to 6 near-threatened species, including spotted-billed, great bald, bengal, black-bellied, and Grey-headed fish eagle and Far Eastern reed, in addition to supporting reptile populations including the endangered Siamese crocodile and numerous freshwater snakes, and although much of the Lake District has been turned into farmland, 200 species of higher plants are still recorded.[21] The Mekong giant catfish, which lives in the Tonlé Sap Lake, is one of the largest freshwater fish in the world. A fisherman caught a Mekong giant catfish weighing nearly 648 pounds in May 2004, but its population has been declining since the mid-1970s. It is currently illegal for fishermen to catch and retain Mekong giant catfish, and only a few are used for scientific research.[22]

As a natural flood reservoir for the entire Mekong River system, Tonlé Sap Lake regulates floods in the lower reaches of Phnom Penh during the rainy season, and is also an important supplement to the dry season flow of the Mekong Delta.[23] In 1997, UNESCO designated the Tonle Sap as a biosphere reserve, but scientists have been concerned that high dams built in southern China and Laos will affect the strength and flow of countercurrents into the Tonlé Sap, reducing the number of fish in the lake. Tonle Sap habitat for nesting, breeding, spawning, and foraging in the floodplain, which will adversely affect fish productivity and overall biodiversity in the Tonle Sap.[24][25]

Forest loss hotspots are located in low floodplain areas where protected areas are located, significant farmland expansion is mainly in the intersection between the lower and upper floodplains, population growth, fuelwood gathering and logging are the main causes of forest loss, intensification of agricultural activities and upstream hydropower development reduces buffers to natural habitats and increases the risk of forest loss.[26] By the 2030s, hydropower development may lead to large-scale changes in habitat, with the area of coastal forests likely to decrease by 82%, while the area of rain-fed habitats may increase by 10–13%.[27] In July 2020, under the influence of the El Niño phenomenon and the impoundment of dams in the tributaries of the Mekong River, the water level of the Tonle Sap Lake hit a record low for the same period in the past 60 years.[28]


Dwellings on Tonlé Sap

The Tonlé Sap Lake District has always been a vital fishing and agricultural production area for Cambodia, and it has largely maintained Angkor, the largest pre-industrial settlement complex in history.[29] While many fish left lakes and ponds to spawn in flooded forests at the onset of floods, the inflow of Mekong floods brought large numbers of fry, which found shelter and food in flooded forests and floodplains.[17]

The approximately 1.2 million people who live in the Tonlé Sap Lake area, which accounts for about 60% of Cambodia's annual freshwater catch of over 400,000 tons, account for 60% of the country's population's protein intake.[30][31][32] Most fish are eaten fresh, and savory and fermented fish paste Prahoc is usually marinated from the least popular fish or leftover fish that cannot be sold fresh.[17] For more than a century, the most productive lake areas have been privatized through a government-lease system of fishing grounds, providing more than $2 million in tax revenue annually.[30]

Floating school on Tonlé Sap

Since Buddhism is against killing, fishermen tend to limit their catch to what they can feed their families. They do not kill the fish with their own hands but wait for the fish to die naturally after they leave the water. At the end of the rice season, people restore canoes that have been in use for hundreds of years or build new canoes when they can't be repaired in temples along the river, in preparation for the boating competition of the water festival. After two days of racing all the canoes come together to celebrate the Naga, the water serpent, who supposedly spit out the lake into the sea at the end of the rainy season,[33] while bringing fish into the Mekong through the Tonlé Sap River.[17]

The area is home to many Cambodians of Vietnamese origin who live in floating villages on boats by the lake.[34] Most of the fishermen of Tonlé Sap Lake are of Vietnamese origin. They have lived in Cambodia for a long time and are the main suppliers of the country's fishery market. They had to flee to Vietnam during the Khmer Rouge reigning era from 1975 to 1979. Only returned after the downfall of the regime and continued to fish in the Tonle Sap.[35]

See also



  1. ^ Agnes Alpuerto (16 November 2018). "When the river flows backwards". Khmer Times. Retrieved 13 July 2020.
  2. ^ "Conservation Project of the Century". Miami Herald. 13 July 1997.
  3. ^ "An Introduction to Cambodia's Inland Fisheries" (PDF). Mekong River Commission. November 2004. Retrieved 15 July 2015.
  4. ^ Seiff, Abby (30 September 2019). "At a Cambodian Lake, a Climate Crisis Unfolds" (Opinion). The New York Times. ISSN 0362-4331. Retrieved 10 December 2020.
  5. ^ a b c d e Oeurng, Chantha; et al. (25 March 2019). "Assessing Climate Change Impacts on River Flows in the Tonle Sap Lake Basin, Cambodia". Water. 11 (3): 618. doi:10.3390/w11030618.
  6. ^ Tjia, H. D. (28 April 2014). "Wrench-Slip Reversals and Structural Inversions: Cenozoic Slide-Rule Tectonics in Sundaland". Indonesian Journal on Geoscience. 1 (1). Institute for Environment and Development University Kebangsaan Malaysia: 35–52. doi:10.17014/ijog.v1i1.174 (inactive 22 June 2024).{{cite journal}}: CS1 maint: DOI inactive as of June 2024 (link)
  7. ^ T. Tamura; Y. Saito; S. Sotham; B. Bunnarin; K. Meng; S. Im; S. Choup; F. Akiba (2009). "Initiation of the Mekong River Delta at 8 ka: Evidence from the sedimentary succession in the Cambodian lowland". Quaternary Science Reviews. 28 (3–4): 327–344. Bibcode:2009QSRv...28..327T. doi:10.1016/j.quascirev.2008.10.010.
  8. ^ D. Penny (2006). "The Holocene history and development of the Tonle Sap, Cambodia". Quaternary Science Reviews. 25 (3–4): 310–322. Bibcode:2006QSRv...25..310P. doi:10.1016/j.quascirev.2005.03.012.
  9. ^ "State of the Basin Report, 2010" (PDF). Mekong River Commission. Vientiane. 2010.
  10. ^ a b Mary Beth Day、D. A. Hodell、Mark Brenner、J. H. Curtis (1 December 2008). "Mid to Late Holocene (5-3 ka) Origin of the Modern Tonle Sap Lake System, Cambodia". AGU Fall Meeting Abstracts. 2008. Bibcode:2008AGUFM.H53C1062D. Retrieved 4 April 2022.
  11. ^ Hydrology. Retrieved 18 May 2015. {{cite book}}: |website= ignored (help)
  12. ^ a b c "Overview of the Hydrology of the Mekong Basin" (PDF). Annual Flood Report. Vientiane: Mekong River Commission. November 2005. ISSN 1728-3248. Archived from the original (PDF) on 13 July 2018. Retrieved 9 March 2021.
  13. ^ britannica (ed.). Tonle Sap. Retrieved 19 April 2022.
  14. ^ McElwee, Pamela; Horowitz, Michael M (1999). Environment and Society in the Lower Mekong Basin: A Landscaping Review (PDF). Binghamton: Institute for Development Anthropology, SUNY. Archived from the original (PDF) on 27 September 2021. Retrieved 4 January 2018.
  15. ^ "Cambodia; 1.4. Hydrology". Water Environment Partnership in Asia (WEPA). Retrieved 12 May 2015.
  16. ^ Kummu, Matti; Dan Penny; Juha Sarkkula; Jorma Koponen (May 2008). "Sediment: Curse or Blessing for Tonle Sap Lake?". Royal Swedish Academy of Sciences. 37 (3): 158–162. doi:10.1579/0044-7447(2008)37[158:scobft];2. PMID 18595269. S2CID 22970198.
  17. ^ a b c d e CASE STUDY No. 3: TRADITIONAL USE AND AVAILABILITY OF AQUATIC BIODIVERSITY IN RICE-BASED ECOSYSTEMS. Food and Agriculture Organization of the United Nations. Retrieved 18 May 2015.
  18. ^ "A. Flora of Cambodia" (PDF). Cambodia Tree Seed Project. Archived from the original (PDF) on 24 June 2022. Retrieved 4 January 2018.
  19. ^ "Semi-evergreen Seasonal Tropical Forest". Retrieved 26 May 2015.
  20. ^ a b "Dry Forest Ecology". World Wide Fund For Nature. Archived from the original on 21 May 2015. Retrieved 20 May 2015.
  21. ^ Campbell, Ian C; Poole, Colin; Giesen, Wim; Valbo-Jorgensen, John (October 2006). "Species diversity and ecology of Tonle Sap Great Lake, Cambodia". Aquatic Sciences. 68 (3): 355–373. Bibcode:2006AqSci..68..355C. doi:10.1007/s00027-006-0855-0. S2CID 28804535.
  22. ^ Sullivan, Michael (7 December 2005). "Tonle Sap: The Flowing Heart of Cambodia" (Audio). NPR. Retrieved 9 March 2021.
  23. ^ Chadwick, M T; Juntopas, M; Sithirith, M (2008). Sustaining Tonle Sap: An Assessment of Development Challenges Facing the Great Lake. Bangkok: The Sustainable Mekong Research Network. ISBN 9789186125066.
  24. ^ "UNESCO conducts consultations at core areas of the Tonle Sap Biosphere Reserve to strengthen conservation and sustainable livelihoods". UNESCO Phnom Penh. 2 February 2021. Retrieved 9 March 2021.
  25. ^ "Technical Note 10" (PDF). Impacts on the Tonle Sap Ecosystem. Mekong River Commission. June 2010. Retrieved 4 January 2018.
  26. ^ Aifang Chen, Anping Chen, Olli Varis & Deliang Chen (8 February 2022). "Large net forest loss in Cambodia's Tonle Sap Lake protected areas during 1992–2019". Ambio. 51 (8): 1889–1903. Bibcode:2022Ambio..51.1889C. doi:10.1007/s13280-022-01704-4. PMC 9200915. PMID 35133565. S2CID 246636436.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Arias, Mauricio Eduardo (2013). "Impacts of Hydrological Alterations in the Mekong Basin to the Tonle Sap Ecosystem". University of Canterbury. Christchurch NZ. doi:10.26021/1497. Retrieved 15 July 2015.
  28. ^ "Ủy hội sông Mekong báo động về mực nước Biển Hồ Campuchia". 越通社. 5 August 2020. Retrieved 5 April 2022.
  29. ^ Thung, Heng L (1994). "Geohydrology and the Decline of Angkor" (PDF). Journal of the Siam Society. 82 (1): 9–14. Archived from the original (PDF) on 29 June 2016. Retrieved 4 January 2018.
  30. ^ a b Van Zalinge, Nicolaas. "Data Requirements for Fisheries Management in the Tonle Sap". FAO Regional Office for Asia and the Pacific. UN FAO. Retrieved 4 January 2018.
  31. ^ "The Tonle Sap Lake and Floodplain". Wildlife Conservation Society. Retrieved 9 March 2021.
  32. ^ Regional Office for Asia and Pacific. "Tonle Sap Fisheries". FAO. Retrieved 30 April 2013.
  33. ^ Didier Fassio (director) (2002). Children of the Seven-Headed Snake: The Sacred Waters of Cambodia (Video). Ampersand. Retrieved 9 March 2021.
  34. ^ "Quyên góp gây quỹ ủng hộ người gốc Việt trên Biển Hồ Campuchia". vietnamplus. 18 October 2020. Retrieved 20 March 2022.
  35. ^ Seiff, Abby (29 December 2017). "When There Are No More Fish". Eater. Retrieved 4 January 2018.

Further reading

  • Kuenzer, C. (2013): "Field Note: Threatening Tonle Sap: Challenges for Southeast-Asia’s largest Freshwater Lake." In: Pacific Geographies 40, pp. 29–31.
  • Milton Osborne, The Mekong, Turbulent Past, Uncertain Future (Atlantic Monthly Press, 2000) ISBN 0-87113-806-9