Some 30,000 man-made barriers, such as hydropower dams, compound the effects of climate change, said Carew-Reid.

“When you take those in concert with climate change, we're looking at a pretty, a pretty negative scenario for fisheries in the basin,” he said.

Scientists at the study's release in Bangkok said dams and other barriers constitute the single largest threat to fish diversity and production.

Laos, controversially, is set to build the first of several hydropower dams on the mainstream of the Mekong.

Hans Guttman, chief executive officer for the Mekong River Commission, warns the extent of damage from the dams is still unknown.

He said, “How much damage is under intense speculation. And, whether all of the dams will be built according to some of the plans or whether some of them will be built and that will then cause a different level of impact, and how the benefits that are generated will be used to compensate or to deal with some of these impacts, is still very much uncertain.”

The U.S. Agency for International Development funded the study as part of its Lower Mekong Initiative.

Alfred Nakatsuma, the regional director of USAID's environment office, said, "The governments in general in these regions are very interested in climate change because the welfare of their people is at stake. And, it's better to address these activities now rather than later when they're surely going to be more costly.”