By Tom Fawthrop, in Chiang Khong, Thailand
As parts of southern China suffer the worst drought in a century, a dramatic fall in the water level of the Mekong has triggered anger and desperation among fishermen and farmers in northern Thailand and Laos who blame Chinese dams on the upstream Mekong for erosion of the river banks, declining fish catches and a damaged ecosystem.
With water levels at their lowest in 50 years, the four Southeast Asian countries badly hit by falling water levels in the mighty Mekong River - Thailand, Laos, Vietnam and Cambodia - will use a summit in the Thai coastal town of Hua Hin this week to confront China, which is blamed for squeezing the river with dams.
China has planned a cascade of eight hydroelectric dams upstream. Three dams are in operation and a fourth named the Xiaowan, which will be the largest, will start operating later this year.
But concessions from Beijing, which is participating as an observer at the summit, are unlikely.
'The Mekong is everybody's river. But when China released water from the dams, the river's level was raised by one metre overnight,' Niwat Roikaew, a leader of 'Love Chiang Khong', a Mekong conservation group, said.
'We have no warning. Now, in the dry season, China does not release water, and the water level, at 0.38 metres, is the lowest in 50 years.'
The shallow water level has caused 21 Chinese boats to run aground and the popular tourist route by boat from Ban Houi Xai to the ancient royal capital of Luang Prabang to be suspended last month. In Vientiane, taps are running dry and there is a severe shortage of drinking water.
Even the usually timid media in communist-ruled Laos dared to criticise Beijing over this unprecedented Mekong crisis, with the newspaper headline 'Mainstream Dams are Killing the Mighty Mekong'.
'The Mekong has changed. This is our mother river but we have lost so much,' Thai environmental activist Niwat lamented.
'Everywhere the people said the drought and the dams had caused the problems.'
Beijing, upset by criticism from the lower Mekong countries, has broken its silence insisting that low water levels can all be explained by climatic factors and the exceptional lack of rainfall since October last year. China's Assistant Foreign Minister Hu Zhengyue told Thai Prime Minister Abhisit Vejjajiva when they met in Bangkok recently that its dams in Yunnan province did not have a significant impact on water levels downstream. An invitation has been sent to the lower Mekong countries to visit the dam in Jinghong.
A UN report last year said the Xiaowan dam on the Mekong at 292 metres high, is the world's tallest.
'Its storage capacity is equal to all the Southeast Asia reservoirs combined,' the report said. 'It can reduce the water volume, the running speed of water, lower water quality and biodiversity in the Mekong River, which runs through six countries.' Young Woo Park, the UN Environment Programme director, warned the six governments to pay attention to the Mekong River, otherwise the future water resources of these countries may be threatened.
Ky Quang Vinh, director of the Ho Chi Minh City's Centre for Observation of Natural Resources and the Environment, told Vietnamnews .net: 'This dam will cause changes in the eco-system in this region. Some flora and fauna species may disappear, including the Irrawaddy dolphin, Mekong giant catfish and others. Eco-regression will be a global disaster.'
The future of the Mekong, flowing south from its source in Tibet 4,350km through Myanmar, Laos, Thailand, Cambodia and Vietnam and essential to the livelihoods of 60 million people, is a matter of deep international concern. It is the eighth longest river in the world but also it ranks second only to the Amazon for its biodiversity and fisheries.
Under pressure from the lower Mekong region to provide data on their dams, China last week agreed to supply the Mekong River Commission with water management data from two out of four mainstream dams on the river - Jinghong and Manwan - but only until end of the drought.
Jeremy Bird, chief executive of the commission's secretariat said last week: 'This is very positive news, as it shows that China is willing to engage with lower basin countries and co-operate in MRC's independent analysis of the flow regime in the upper part of the basin.'
Bird also reported that the commission's analysis 'has shown that the low flows are caused by extremely low rainfall, rather than any man-made infrastructure on the river'.
Environmentalists are not convinced that the commission report tells the whole story. Carl Middleton from the 'Save the Mekong' campaign - an international network of NGOs from Thailand, Cambodia and Vietnam - asked: 'How can the MRC be so sure that China's dams aren't exacerbating the drought, when China is still only releasing partial data sets? The most important data detailing the Xiaowan dam reservoir's water levels is still being withheld.'
What is undeniable is the scramble for hydroelectric power and the harnessing of nature has turned the Mekong into a river of controversy and potential conflict over increasingly scarce water resources.
Thai conservationist and former senator, Tuenjai Deetes, says there is only one solution.
'It is time for a six-party agreement on sharing the waters of the Mekong. I don't see any mechanism to protect the Mekong.'
1 The Mekong at 4,350km long is the lifeblood for 60 million people in six countries, who depend on it for drinking water, transport, irrigation and fishing
2 Water levels in the Mekong have dropped to as low as 0.38m, with levels at mainstream measuring stations in Laos and northern Thailand below those in 1992
3 Conservationists say 11 hydropower dams, either partly built or already completed, in southern China are choking supplies
4 The Mekong River Commission (MRC) said China would share data from its upstream monitoring stations
5 Almost 6 million people and 3.6 million head of livestock are short of drinking water after the drought in Yunnan province, where the Mekong is known as the Lancang River