Tonle Sap, Cambodia

Lake Locations:

Cambodia -

Also known as:  Great Lake, Tonle Sap Lake

The largest freshwater lake in Southeast Asia, Tonle Sap is far more than ‘just a lake’. It is the lifeblood of northwestern Cambodia and an ecological treasure revered by environmentalists. The name Tonle Sap means ‘large freshwater river’, an apt description.

During the dry season, Tonle Sap is a modest 1,050 square miles of shallow water about four feet deep. The Tonle Sap River fills a shallow basin before heading downstream to join the Mekong River and eventually drain to the Mekong Delta and the sea. During the heaviest part of the monsoon season, the lake swells to cover over 6,175 square miles 30 feet in depth. The lake floods fields and forests when the river’s flow reverses. The Mekong River, swollen by snow melt from the Himalaya Mountains and heavy monsoon rains, forces water back upriver and onto the floodplain. The annual flooding has continued for thousands of years, giving rise to a diverse and prolific ecosystem that supports about 200 species of birds, 149 species of breeding fish and well over a million people.

When the Tonle Sap floods the forests and fields of the floodplain, excellent conditions for spawning fish and feeding birds and mammals are created. The native people, mostly Khmer and Vietnamese, have created a subsistence economy based around the lake’s bounty. Nearly 70% of the native diet consists of fish. The rest is primarily rice cultivated on the flood plain during the dry season. Villages built on floating platforms or stilts serve to keep the locals near their food sources and their fishing. The lake has long been known as habitat to the Mekong Catfish reaching eight feet long and over 600 pounds-often called the world’s largest freshwater fish. The area holds a variety of reptiles, including nearly-extinct Siamese Crocodiles and the world’s largest variety of freshwater snakes. Some of the endangered and threatened bird species found here are the Manchurian reed warbler, grey-headed fish eagle, spot-billed pelican, Bengal florican and greater adjutant.

Although the water quality doesn’t show signs of serious threat, fish stocks have declined. The Mekong Catfish has declined 95% from its former numbers in the mid-70s. Overfishing may be partially to blame, and speculation gives voice to a fear that dams built upstream on the Tonle Sap and the Mekong have reduced the spawning migrations of the giant catfish. In 2001, the entire lake and surrounding provinces were decreed the Tonle Sap Biosphere Reserve. Fishing seasons and regulation have been instituted, and the Mekong catfish is no longer allowed to be caught except for biological study purposes. The provinces of Battambang, Kampong Thom, Preah Vihear, Banteay Meanchey, Otdar Meanchey, Siem Reap, Pailin, Pursat and Kampong Chhnang are now closed to fishing during the fish spawning season. All areas within the Reserve have worked to prevent bird and mammal poaching of the threatened species. Several areas have been set aside as bird sanctuaries and wildlife reserves, including the Preak Toal Bird Sanctuary protecting the large colonies of birds on the Tonle Sap itself. International groups have worked to assist the already impoverished local populations to replace lost income through marketing native crafts and guiding ‘eco-tours’ and to enlist them in the effort to preserve their local biodiversity.

Tourism is becoming a larger part of the local economy as visitors flock to take boat tours on the lake. Boat tours visit floating villages such as Chong Khneas near the town of Siem-Reap where residents’ homes, schools and markets are all built on floating platforms. Villagers wait eagerly with boats to take willing tourists for a cruise on the lake and often offer items for sale such as food or trinkets, along with a universal plea for ‘donations’ to a school, local charity or other cause. Because these activities are not regulated or controlled, most knowledgeable travelers suggest hiring an experienced and licensed tour guide to handle setting up and leading tours. One large tour boat offers luxury cruises serving three-course meals. The nearby town of Siem-Reap is an excellent modern small city to serve as a home base for sightseeing in the area. Several modern hotels are available along with local offerings of somewhat questionable credibility. Again, an experienced tourist agency may be the best bet for setting up tours and lodgings.

Siem-Reap is served by an airport and is less than 10 miles from Tonle Sap. Other attractions in the area include the ancient palaces at Angkor Archeological Park only about three-and-a-half miles from the center of the city. The extensive site can actually take several days to fully explore and is decorated with amazing carvings and depictions of Hindu gods. The entire site covers over 150 square miles and is still in the process of being recovered from the surrounding forest and overgrowth. Contained within the park are temples built when various areas served as the capitals of several Khmer regimes and includes the well-known Angkor Wat.

Only 30 miles from Siem-Reap, Kulen Mountain National Park is the site of an isolated mountain considered the birthplace of the Khmer Empire. Graced with statuary, temples and carvings located on the bed of a sacred pool, the park is a favored local destination for picnics and walking tours. Native animals that may be seen in the park include leopard, tiger, Asian elephant, rhinoceros, monkey and deer. Many other temples can be visited in the area, and bus transportation is available.

Not far from Seim-Reap, the Ang Trapeng Thmor Sarus Crane Reserve serves as habitat for the increasingly rare sarus crane. A few companies now offer eco-tourism trips featuring selected native homestays, local food offerings, handicrafts and forays onto Tonle Sap to visit the bird breeding areas and examine interesting native flora. Cambodia is the lifetime adventure you dreamed of-exotic, historic and singularly unique in both culture and surroundings. Come and taste life on the Tonle Sap and marvel at hundreds of years of human acclimation to nature’s patterns. See why local Cambodians call Tonle Sap the ‘Great Lake’. You’ll fill memory books that will enrich the family library for years to come.

Things to do at Tonle Sap

  • Vacation Rentals
  • Fishing
  • Boating
  • Picnicking
  • Wildlife Viewing
  • Birding
  • National Park

Fish species found at Tonle Sap

  • Catfish

Tonle Sap Photo Gallery

Tonle Sap Statistics & Helpful Links

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Lake Type: Natural Freshwater Lake, Not Dammed

Surface Area: 666,880 acres

Normal Elevation (Full Pond): 14 feet

Average Depth: 4 feet

Maximum Depth: 30 feet

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Trophic State | LakeLubbers

Trophic State measures the level of algae and nutrients in a lake.

An oligotrophic lake is very clear (blue in color) and does not support much plant or fish life. A hyper-oligotrophic lake is the clearest of all lakes, and is nearly devoid of plants and fish.

A mesotrophic lake is slightly green and supports a moderate degree of plant and fish life. A lake's most desired trophic state is generally this mid-point - the mesotrophic state.

A eutrophic lake is somewhat murky and supports a large amount of plant and fish life. A hypereutrophic lake is clouded with algae, plant life, and fish life. A eutrophic or hyper-eutrophic lake can be difficult to navigate by boat - and is often an unpleasant place to swim.

The use of phosphorus-rich and nitrogen-rich fertilizer on lawns and golf courses surrounding a lake can cause it to become eutrophic or hypereutrophic.


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Catchment or Drainage Area | LakeLubbers

This is the surrounding area that drains into a lake, including land, rivers and their tributaries. This is also known as the lake's "catchment basin".

Small lakes at the highest peaks of mountains have small drainage areas. The world's oceans have the largest drainage areas.


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Lake-Area Population | LakeLubbers

This is the estimated number of people who live in a house with a view of a lake, plus those who self-describe the lake as their home, for example: "I live at Smith Mountain Lake."


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Water Residence Time | LakeLubbers

This is the estimated time that it takes for an amount of water equal to the entire volume of a lake to flow out of - or evaporate from - the lake.

Residence Time can be as short as a few days for fast-flowing small lakes, and can exceed 100 years for slow-flowing large lakes.


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Completion Year | LakeLubbers

This is the year that a reservoir was first filled to the reservoir's normal elevation - or the year that a natural lake was first dammed. A large reservoir can take more than a year to fill after its dam is first closed.

The Grand Anicut in southern India is generally considered the world's oldest dam that still operates. Grand Anicut was constructed in the second century BC. It now impounds an irrigation network that includes roughly one million acres.

You can find many of the the world's newest reservoirs on LakeLubbers. Many of the world's oldest reservoirs appear on the last page of that list.


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Water Volume | LakeLubbers

This is the estimated volume of water that a lake contains -- measured at the lake's normal elevation. By this measure, the world's largest freshwater lake is Siberia's Lake Baikal.

You can find many of the the world's largest lakes (by water volume) on LakeLubbers.

Water Volume can be measured in acre-feet, in cubic miles, or in cubic kilometers. One acre-foot is the amount of water needed to cover one acre (43,560 square feet) to a depth of one foot. One cubic mile equals 3,379,200 acre-feet. One cubic kilometer equals 810,713 acre-feet.

1 acre-foot is equal to 325,851 US gallons. Siberia's Lake Baikal contains about 6,276,367,740,000,000 gallons of freshwater - nearly 1 million gallons for every living person on earth.

The other - and more widely used - measure of a lake's size is the lake's surface acreage. By that measure, the world's largest freshwater lake is North America's Lake Superior.


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Maximum Depth | LakeLubbers

This is the estimated greatest depth of the water in a lake -- measured at the lake's normal elevation. The world's deepest lake is Siberia's Lake Baikal; that lake's maximum depth is estimated at 5,314 feet.

You can find many of the the world's deepest lakes on LakeLubbers. If you select the last page of that list, you will find the (maximum depth of) the shallowest lakes in our database.


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Average Depth | LakeLubbers

This is the estimated average depth of the water in a lake -- measured at the lake's normal elevation. If the water volume and surface area of a lake are known, an estimate of the lake's average depth can be calculated:

Water volume ÷ Surface Area = Average Depth

Example: 1,000,000 acre-feet ÷ 20,000 acres = 50 feet average depth


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Maximum Elevation | LakeLubbers

This is a lake's highest water level, measured by the lake's surface distance above sea level, that can occur during flooding. A lake's highest possible maximum elevation is usually the top of the lake's dam or spillway.

At lakes that include residential development, government regulations usually forbid the construction of homes below a lake's maximum elevation.


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Minimum Elevation | LakeLubbers

This is a lake's lowest water level, measured by the lake's surface distance above sea level, that can be reasonably expected to occur. Low lake levels can occur due to deliberate seasonal draw downs for irrigation or impending snow melt, reduced water inflows, drought and evaporation, residential or commercial water demands, and hydropower generation.

Some lakes' minimum and maximum elevations are virtually the same. Lakes that generate hydropower may vary by several feet - according to power demand. Lakes whose primary purpose is to prevent flooding can seasonally vary by 100 feet or more.

When some lakes reach their minimum elevation, their boat ramps may not be long enough to permit boat access - and boats docked on shallow parts of the lake may end up on dry ground. In those cases, kayakers and shore-based anglers may be among the few happy recreational users of the lake.


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Normal Elevation | LakeLubbers

This is a lake's normal water level, measured by the lake's surface distance above sea level. For a reservoir, this water level is also known as "full pond" or "full pool".

You can find many of the world's highest-elevated lakes on LakeLubbers. Lakes with the lowest elevations (known by LakeLubbers) are shown on the final page of that list.


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Shoreline Length | LakeLubbers

This is the length of the exterior shoreline around a lake - measured at the lake's normal elevation. The shoreline length can be considerably shorter or longer when lake water levels are lower or higher than normal.

A lake with many coves has a much longer shoreline than a lake of similar surface area that is nearly circular in shape.

When known, the shoreline miles that we report in our statistics include only the lake's exterior shoreline, and exclude the shorelines of islands located within a lake's boundaries. In lakes with many islands, those islands' combined shorelines may exceed a lake's exterior shoreline.

You can find many of the world's longest-shoreline lakes on Lakelubbers.


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Surface Area | LakeLubbers

This is the area (acreage, square kilometers, etc.) of the top surface area of a lake - measured at a lake's normal elevation. The surface area can be considerably smaller or larger when lake levels are lower or higher than normal. North America's Lake Superior is the world's largest freshwater lake by this measure.

The other measure of a lake's size is the lake's water volume. By that measure, the world's largest freshwater lake is Lake Baikal in Siberia.

You can find many of the world's largest lakes (acres) on Lakelubbers. There is no widely-accepted minimum surface area that defines a lake. What Lakelubbers describes as a lake, you might call a pond. The smallest lake that Lakelubbers currently includes is Hawaii's 2-acre Lake Waiau.


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Water Level Control | LakeLubbers

This is the organization that controls water releases or outflows from the lake or reservoir. In the USA, this is often the US Army Corps of Engineers, a power company, a municipal water system, an irrigation district, or a paper manufacturing company. In the case of private or gated lakes, a homeowners' association may be the lake's controlling authority.

Many lakes cross borders, including North America's Great Lakes. The control of such lakes and their coveted freshwater may be amicably shared - or hotly disputed.

"Water wars" continue at many lakes as growing populations and crop irrigation needs compete for the freshwater that lakes contain.


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Lake Type | LakeLubbers

There are 3 basic types of lakes that are currently included on LakeLubbers. 2 types may be dammed or not dammed, producing 5 classifications.

- A Reservoir is a man-made freshwater lake that is usually created by damming rivers.

- A Natural Freshwater Lake occurs naturally - often by glacial activity - and has a salinity of less than 30 parts per thousand. It may be dammed to produce electricity or for other reasons.

- A Natural Saltwater Lake occurs naturally and has a salinity of more than 30 parts per thousand (ppt). It may be dammed.

"Brackish" water may be categorized as freshwater or saltwater, depending on its salt content (salinity). Oligohaline water has less than 15 ppt of salt. Mesohaline water has 15-29 ppt. Polyhaline has 30-335 ppt.


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