The roaring currents of the Mekong have long enchanted travellers, inspired explorers and sustained about 65 million people living off the world's largest freshwater fisheries.
But environmentalists warn that the 'Amazon of Asia' - the river with the second-richest biodiversity in the world - is under dire threat from hydropower dams, including the latest to be proposed: the Xayaburi dam in Laos. Authorities in Laos have put their faith in hydropower as a formula to lift the nation out of chronic poverty by selling electricity to Thailand and Vietnam.
The Laotian government notified the Mekong River Commission in September of its plans to build a dam at Xayaburi, in co-operation with a Thai private company.
It has triggered alarm bells among environmental scientists, non-government organisations and river communities about a headlong rush into dam building before the environmental impact has been fully understood.
'There is a very fast pace of hydropower development, passionately fast,' Juta Sarkkalen, a Mekong specialist from Helsinki and based in Vientiane, said. 'We need a time out. We need a moratorium on dams to consider a different strategy of development.'
China has already built four dams on the Lancang (the Chinese stretch of the Mekong), including the tallest high-arch dam in the world, at 292 metres.
Four more in China and 11 dams projected in Laos and Cambodia have triggered major controversy.
'The two dams, Xiaowan and Nuozhadu [the next Chinese dam to be built in Yunnan ], will impact the flow regime of the entire system all the way down to the delta in Vietnam,' warned Dr Philip Hirsch, director of The Mekong Research Centre at the University of Sydney.
A Laotian environmental activist provided another view on the pros and cons of dams along the Mekong.
'When you talk with local people, they say 'well, development of dams brings brightness in the eyes, but darkness in the heart',' the activist said.
A warning has also been issued by the WWF that building of the Xayaburi dam would almost certainly wipe out the endangered giant catfish that can reach up to 300kg in weight. A further 41 species of fish face extinction. Downstream in southern Laos and Cambodia a colony of Irrawaddy dolphins would stand little chance of survival.
A Thai parliamentary committee is studying the impact of dams on the Mekong, chaired by Kraisak Choonhavan, the former senator and deputy leader of the ruling Democrat Party.
'The effect of the Xayaburi dam will be a devastating on all the countries, Laos, Thailand, Cambodia and Vietnam,' Kraisak said.
China is not a member of the Mekong River Commission (MRC), and its unilateral dam programme has been widely criticised. But Deputy Foreign Minister Song Tao, who attended a landmark meeting of Mekong countries in Hua Hin, Thailand, earlier this year dismissed fears that the hydropower dams had exacerbated a severe regional drought.'
'China itself is also a victim of the present severe drought,' Song told the heads of state of Thailand, Laos, Cambodia and Vietnam, referring to the worst drought in a century in four southwestern provinces, with more than 24 million people short of drinking water,
In an unusual diplomatic gesture, China earlier in the year also began releasing to its neighbours closely held information on daily dry-season data from two hydro-meteorological stations in Yunnan. It has also invited MRC countries to visit its hydropower stations.
In case of the Xayaburi dam, Laos is a member of the MRC, and as such, the project becomes the first test case for treating a Mekong dam project as an international issue.
A consultation process comes into effect between the four on whether the dam should be allowed to go ahead.
Many of the downstream dams will block fish migration, especially the Don Sahong with its site near the spectacular Khone Waterfall sitting astride the only passable channel for fish swimming up from Cambodia and Vietnam.
For Cambodians who depend on freshwater fisheries for more than 80 per cent of their protein intake, dams that block fish migration could be a disaster for both food security and nutrition.
Professor So Nam, of the Institute of Fisheries in Phnom Penh, said: 'People totally depend on fish. We have one of the highest rates of fish consumption in the world. Every year Cambodian people catch about half a million tonnes of fish. It provides more than 6 million people with employment.' The MRC views dam development, as the need to balance opportunities against risk.
The final report of independent consultants to the commission has made clear the risks inherent in going ahead with more dams. Total fish production at risk of mainstream dam development ranges between 700,000 tonnes and 1.4 million tonnes.
Many activists and scientists in Vietnam also have spoken out against more dams.
'For Vietnam, the existing and proposed dams on the mainstream and tributaries of the Mekong River, certainly pose tremendous threats,' Trinh Le Nguyen, the executive director of PanNature, a nature conservation group, said.
An NGO network covering 24,000 people in northern Thailand has called on the Thai prime minister to cancel commitments by Thailand's electricity company, EGAT, to buy electricity from Xayaburi.
The decision on the dam could seal the Mekong's fate for generations. Will its great resources be solely channelled into power generation, or will decision-makers count the potential costs.
The strategic environmental assessment (SEA) report commissioned by the MRC recommends that all further dam projects be deferred for the time being.
Hirsch insists that this all-important issue 'should only be decided on the best possible evidence. Lets hold off for at least 10 years. At least 10 years'.
The Mekong is in the balance as development and conservation collide
The percentage of protein Cambodian people get from freshwater fish is: 80