The Xayaburi dam, the first of eleven dams planned for the mainstream of the lower Mekong River, will likely reduce ecosystem service values and undercut livelihoods of people living in Thailand, Lao PDR, Cambodia, and Vietnam. A recent Mekong River Commission study reports that the cumulative impacts of the planned dams in Lao PDR could disrupt the lifecycles of migratory fish, block access or destroy spawning grounds, and reduce catch by 270,000 to 600,000 metric tons.
This is especially significant because the Mekong is one of the most biodiverse and productive rivers on Earth. It is a global hotspot for freshwater fishes: over 1,000 species have been recorded there, second only to the Amazon. The Mekong River is also the most productive inland fishery in the world. The total harvest of approximately 2.5 million metric tons per year is valued at $3,600,000,000 to $6,500,000,000.
The Xayaburi dam also poses a serious threat to several of the largest, and rarest, freshwater fish in the world, including the critically endangered Mekong giant catfish (Pangasianodon gigas), the critically endangered giant pangasius (Pangasius sanitwongsei), and the endangered seven-striped barb (Probarbus jullieni).
Evidence suggests that these species, particularly the Mekong giant catfish and giant pangasius, are vulnerable to threats from Xayaburi dam because of their migratory behavior, requirements for specific water quality and flow, and complex life history, which is dependent on seasonal floods.
The official environmental impact report for the Xayaburi project does not assess the dam’s effects on these, and many other migratory and Red Listed, species. Depending on the scale of migrations and location of spawning sites, the Xayaburi could cause the extirpation of the Mekong’s giant fishes over a large (hundreds of kilometers) area and put basinwide populations on a steep trajectory of decline.
Several groups, including the Mekong River Commission, have called for a ten-year moratorium on mainstream dams to better assess the long-term social and environmental costs of such projects. Such large-scale assessments have become common on rivers where managers seek to rebuild migratory fish stocks but are urgently needed at the outset of projects to avoid unnecessary destruction of ecosystem services and costly restoration efforts. The long-term viability of vulnerable fish populations – and people who depend on fish for food – is dependent on the ability to minimize the impacts of any mainstream dams built on the lower Mekong River.