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.

[2] In the 21st century, the lake and its surrounding ecosystems are under increasing pressure from deforestation, infrastructure development and climate change.

[6] The lower Mekong plain used to be a bay, and the sea level rose rapidly at the end of the last glacial period.

[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).

[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.

[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.

[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] 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.

[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.

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.