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Published: April 14th 2011
Cambodia's two dominant geographical features are the Mekong River and the vast lake, Tonle Sap - the largest freshwater lake in Southeast Asia and an incredible natural phenomenon. At Phnom Penh the Mekong splits into three channels: Tonle Sap River which connects with Tonle Sap Lake; the Upper River (called the Mekong or in Vietnamese, Tien Giang) and the Lower River (Tonle Bassac, or Hau Giang in Vietnamese). The rich sediment deposited during the Mekong's annual wet-season flooding has made central Cambodia incredibly fertile. This low lying plain is where the vast majority of Cambodians live, fishing and farming with the rhythms of the monsoon.
From mid May to early October (the wet season)the level of the Mekong rises rapidly, backing up Tonle Sap river, causing it to flow into the Tonle Sap Lake. During this period Tonle Sap Lake expands to five times its size and 70 times its volume and provides a huge percentage of Cambodians' protein intake; 70% of which comes from fish. Around the start of October, as the water level of the Mekong begins to fall, the Tonle Sap River reverses its flow, draining the waters of the lake back into the Mekong. This amazing process makes the Tonle Sap one of the world's richest sources of freshwater fish, as flooded forest makes for fertile spawning grounds. The fishing industry supports about one million people in Cambodia and an individual fisher's catch on the great lake can average 100kg to 200kg per day in the dry season.
But this ecosystem is under threat. Dams upstream - including Sambor Dam near Kratie, and Si Phan Done in southern Laos may effect the annual monsoon flooding of the Mekong. Even a drop in just 1m in wet season water levels would result in around 2000 sq. km less flood area around Tonle Sap. This would lead to less nutrient rich silt deposits and would have disasterous consequences for Cambodia's farmers. Migratory patterns of fish may also be affected. Some environmentalists claim that the fish population of the Mekong and perhaps the Tonle Sap might be halved. Illegal logging poses a further threat. In the mid 1960's Cambodia was reckoned to have around 90% of its original forest cover intact. Estimates today vary but it's likely that only about 30% remain. Topsoil loosened in upland Cambodia flows down the country's rivers in the form of silt into the great lake. The shallowest areas may eventually begin to silt up - which would have disasterous consequences not only for agriculture in Cambodia but also for neighbouring Vietnam.
Tonle Sap now has protected biosphere status - but with the Cambodian population growing by 300,000 a year and regional energy needs spiralling ever upwards; the need to generate hydroelectric power becomes ever greater - this may not be enough to protect this unique eco system.
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