BANGKOK, April 19 (Reuters) - Officials from Thailand, Cambodia, Laos and Vietnam met on Tuesday to debate a plan to build a huge dam across the Mekong River, a project experts warn could trigger a food security crisis in the region. [ID:nL3E7FI0YS]

The proposed $3.5 billion, 810-metre (2,600-ft) Xayaburi dam in northern Laos is being touted as a major step for green energy, but ecologists and environmentalists believe millions of livelihoods and regional stability are at stake if the dam goes ahead.

WHAT ARE THE EXPERTS SAYING?

They warn dozens of migratory fish species will become extinct if the dam is built. Fish stocks will dwindle, affecting fishermen and local people who live off Southeast Asia's biggest waterway.

The dam could prevent the movement of fertile silt needed to replenish agricultural land. Parts of the Mekong river in Thailand, Vietnam and Cambodia could be turned into virtual reservoirs and crops vital to domestic consumption and exports, such as rice, could be starved of nutrients.

They also say the proposed fish ladder -- which allows fish to move through the dams -- was poorly designed and is likely to fail. A decline in stocks would have an impact on the human protein intake and revenues for farmers and fishermen would be significantly reduced, forcing many to relocate.

A study by the Mekong River Commission (MRC), an inter-government agency set up to coordinate dam projects, says the Xayaburi dam could lose 60 percent of its capacity within 30 years due to sedimentation.

SO WHY IS LAOS SO EAGER WANT TO GO AHEAD?

Laos's ambitious Communist government wants to shed its status as one of the world's poorest countries within the next decade and is aggressively pursuing hydropower as a means to generate income and raise its international profile. The sparsely populated nation has 10 projects so far and 60 more in the pipeline.

It has agreed deals to generate power for Thailand, Cambodia and Vietnam and relishes its newfound reputation as the "battery of Southeast Asia". By producing hydroelectric power, Laos sees itself as increasing its political clout and reducing its dependence on its neighbours.

Laos insists green energy is the way forward and has ignored the chorus of criticism. It is "excited" about Xayaburi and stands by its view that environmental and human impacts will be minimal.