Laos is preparing to build a very large dam across the main flow of the Mekong, in Xayabury, halfway between Luang Prabang and Vietniane. The other members of the Mekong River Commission, Cambodia and Vietnam, stand to lose much from the damming of the main flow of the Mekong.
As the ecosystem of Cambodia's central plain largely depends on the yearly high-water cycle of the Mekong: as the Tonle Sap lake only drains its own river basin --no main river feeds it--, it depends on the high waters of the Mekong and the fast flow of their drainage to naturally dredge the Tonle Sap river that connects it to the Mekong and prevent the lake from silting up. If the Tonle Sap lake were to silt up, it would easily turn into a swamp and soon would be rendered unhealthy, which would be a "disaster of food and nutrition security" for the 13 million inhabitants of Cambodia.
Vietnam is calling for deeper research into the impact of this dam too, as the Mekong delta, nearly 2000 km downstream from the planned dam, is host to about twenty million inhabitants (four times as many as Laos) and produces more than half the agricultural output of the whole of Vietnam. Endangering the livelihood of the Mekong delta would also entail tragic consequences for Vietnam. Water issues,
But Laos keeps a solid stance: Xayaboury is in Laos, this 1260 MW hydro-power project is a commercial agreement with Thailand and as it is located on Lao territory, Laos is competent to make the decisions regarding the project. Laos is backed in this by its powerful neighbour Thailand, which is both an investor into the power plant and the main client to the plant's electricity production. As it does not stand to lose from the Mekong's damming as it borders Thailand only upstream from the dam, Thailand is strong-arming the debate.