Tonle Sap, The Great Lake

We took a boat down the Sangker River across Tonle Sap ( the largest freshwater lake in Southeast Asia), a designated UNESCO biosphere in 1997. During the monsoon season, water is pushed up from the Mekong river into the lake, flooding surrounding fields and forests making Tonle Sap one of the most productive inland fisheries in the world and extremely important for the Cambodian economy. However, in the dry season (roughly February to May), the receding waters can make it impossible to travel by boat.

We had just enough room to pass other boats gunwale to gunwale on our way to the floating villages, which are anchored into the lake mud by the use of bamboo poles. Trees have been sacrificed along the borders of the lake to be burned for fuel causing serious deforestation which the government is attempting to address. Diarrhea is a constant problem for the children living on the water because they drink the water that they are also using for sewage, washing, and fishing. Crocodiles prowl the edges of the huge lake.

Here is some more information from Wikipedia (trust me, it’s accurate!):

The Tonlé Sap is unusual for two reasons: 1) its flow changes direction twice a year, and 2) the portion that forms the lake expands and shrinks dramatically with the seasons. From November to May, Cambodia’s dry season, the Tonlé Sap drains into the Mekong River a Phnom Penh. However, when the year’s heavy rains begin in June, the Tonlé Sap backs up to form an enormous lake.

For most of the year the lake is fairly small, around one meter deep and with an area of 2,700 square km. During the monsoon season, however, the Tonlé Sap river, which connects the lake with the Mekong river, reverses its flow. Water is pushed up from the Mekong into the lake, increasing its area to 16,000 square km and its depth to up to nine meters, flooding nearby fields and forests. The floodplain provides a perfect breeding ground for fish.

The pulsing system with the large floodplain, rich biodiversity, and high annual sediment and nutrient fluxes from Mekong makes the Tonlé Sap one of the most productive inland fisheries in the world, supporting over 3 million people and providing over 75% of Cambodia’s annual inland fish catch and 60% of Cambodians’ protein intake. At the end of the rainy season, the flow reverses and the fish are carried downriver.

National and local observers often state that the Tonlé Sap Lake is rapidly filling with sediment. However, recent long-term sedimentation studies show that net sedimentation within the lake proper has been in the range of 0.1-0.16 mm/year since ca. 5500 years before present (BP). Thus, there is no threat of the lake filling up with sediment. On the contrary, sediment is not a threat to the lake but an important part of its ecosystem, providing nutrients that drive the floodplain productivity].

The reversal of the Tonlé Sap river’s flow also acts as a reservoir as the Mekong Delta restricts the flow to the South China Sea. During the dry season (December to April) the Tonlé Sap Lake provides around 50% of the flow to the Mekong Delta in Vietnam.

• Cambodia