Massive hydroelectric projects in China and Vietnam are threatening to wreak havoc along the lower stretches of the Mekong River, environmentalists warn, saying foreign dams could do more damage to Cambodia's fragile ecosystem than the Kingdom's own nascent hydropower sector.

Hydropower development on the upper reaches of the Mekong River in southern China is a particular long-term concern for all the countries of the lower Mekong basin, according to Carl Middleton of the US-based International Rivers Network.

China's thirst for electricity has led to the planning of eight giant projects on the upper Mekong, two of which are currently operational and three of which are under construction.

"[The planned dams] can be expected to significantly alter the distribution of dry and wet season river flows, as well as result in daily water level changes," Middleton said, adding that "even subtle changes can bring about large and unexpected impacts on ecosystems."

"Fish are central to both the food security and the national economy of Cambodia. Therefore threats to these fisheries should be considered with the seriousness they deserve," he said.

Environmentalists say one major problem is the lack of consultation between the developers and local communities that will be affected by the projects.

"A public decision-making process about a dam's proposed development is critical," Australian academic Milton Osborne wrote in a 2004 study, Rivers at Risk. "And clearly this public process has not happened in the case of China's mainstream dams."

Environmental groups have also observed problems stemming from the three dams currently operating on the Se San River, a major Mekong tributary in Vietnam's Central Highlands.

A July 2007 report issued by the Rivers Coalition in Cambodia (RCC) said the Yali Falls dam in Vietnam "has significantly disrupted the Se San River's flow in downstream Cambodia, where more than 28,000 people depend on the river for their drinking water, irrigation, fishing, livestock-watering and transportation."

Roman Mleac, 56, from Pawdal village in Ratanakkiri province, less than 6km from the Vietnamese border, told the RCC that "water levels [on the Se San] are changing every day. The water rises in the morning and at night the water falls.... The change is around six meters."

Despite concerns voiced by community leaders in Ratanakkiri and Stung Treng provinces, who have requested they be consulted on any future developments, state-run power supplier Electricity of Vietnam has plans to build two more dams on the Se San.