BBC News 19 April 2011
By Guy DelauneyBBC News, Cambodia
The four member countries of the Mekong River Commission are meeting to make a final decision on whether to allow the construction of a controversial dam.
The proposed hydropower project at Xayaburi would be the first to be built on the main-stream of the lower Mekong.
Laos is hoping to become "the battery of southeast Asia".
The Mekong River Commission's ruling may determine whether the river stays a food resource for millions of people, or becomes a source of power instead.
Laos's plans mean using its rivers to generate electricity for export, thereby gaining income to develop the country - which is fine when the waterways in question are wholly within Laos.
It is rather more complicated when they are shared with neighbouring countries, as is the proposed Xayaburi dam and power station.
It would be the first hydro project on the mainstream of the lower Mekong.
Countries downstream are understandably concerned about the possible effects on them.
In Cambodia, fishing communities are worried that they might see a disastrous decline in stocks.
Sen Salim lives in a fishing community on the outskirts of Phnom Penh.
"This river is very important - when there are many fish it helps us to make a better living. When there are fewer fish it is bad for us," he says.
"If they made a dam in the big river, it would block the water flow - then the fish wouldn't be able to get through to migrate and breed."
It is a matter of national importance.
Fish provides about four-fifths of the average Cambodian's protein intake, and millions of people rely on the Mekong for their livelihoods.
World Wildlife Fund says the consequences of mainstream dams have not been studied properly.
The Mekong River Commission's own report suggested a 10-year moratorium on construction.
That has been backed by community organizations - they are suggesting alternative ways of generating electricity.
"We could have solar energy, biomass, bio-gas - and also small dams not on the mainstream. The mainstream would have a big impact on millions of people.
"It's going to be a disaster if the decision is not considered carefully," said Chhith Sam Ath from the umbrella group, the NGO Forum on Cambodia.
Cambodia is planning mainstream Mekong dams of its own and many more have been proposed in Laos.
The decision on the Xayaburi project is the key to them all.