GIANT dams on the Mekong river in southeast Asia are being blamed for sudden bizarre fluctuations in the flow of one of the world鈥檚 longest rivers. Environmentalists say dam operations in China threaten the livelihoods of fishing communities in Thailand, Laos, Cambodia and Vietnam.
The Mekong River Commission, an intergovernmental body that China has refused to join, called an emergency meeting last week to discuss the crisis on the river. Afterwards it sent an official letter to China demanding information about the operation of its dams, which block the headwaters of the river in Yunnan province.
The 4500-kilometre river has seen record lows since January, and strange and unprecedented fluctuations in its levels. China has built two large hydroelectric dams on the river (which is called the Lancang Jiang in China): the Manwan and Dachaoshan.
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鈥淭here is an assumption that the two dams are the cause of the situation,鈥� says Surachai Sasisuwan, director of the commission鈥檚 water resources department.
The last time the Mekong saw exceptionally low flows was in 1993, during the filling of the Manwan dam. The even larger Dachaoshan dam, completed in 2003, could be behind the new lows. Two more dams are under construction, and at least another four are at the planning stage. China is also blasting rapids along the river.
鈥淪ince the dams began operating, river levels have gone up and down much faster,鈥� the commission鈥檚 Hans Guttman told 快猫短视频 late last year. While only 25 per cent of the river鈥檚 annual flow comes from China, the proportion normally reaches 50 to 70 per cent in the dry season, he said.
A poor monsoon flood season last summer probably also contributed to the new low levels of the river. The annual flood is vital to one of the world鈥檚 biggest inland fisheries. Cambodians alone catch 2 million tonnes of fish a year from the river.
The Chinese dams aim to tap the huge potential of the river for hydroelectric power. But biologists say they could kill off the fisheries for good. Most of the fish reproduce in forests in central Cambodia, which flood every year when the Tonle Sap, a tributary of the Mekong, is swamped by the main channel, reverses direction and backs up into the forests. If the reversal of the Tonle Sap鈥檚 flow were to cease it would be disastrous for fisheries.
There are hints that fish stocks in the Mekong, home to the increasingly rare Mekong catfish that grows to three metres long, are already depleted. 鈥淭he fish catch is miserable; this has been a bad year,鈥� says Eric Baran at the Phnom Penh office of WorldFish, an international research centre.
Researchers admit that Chinese dams are not alone in altering the flow of the Mekong. Downstream countries take significant amounts of water to irrigate rice crops. But says Guttman: 鈥淭he Chinese dams are so large, they are changing everything.鈥�