Governance of large river basins in mainland SEA is being challenged by a significant resurgence in large-scale hydropower projects. The first of 11 mainstream dams on the lower Mekong – Xayaburi – is under construction in Laos with completion scheduled for 2019. The project will join six mega-dams already in operation in the upper part of the Lancang/Mekong mainstream in Chinese territory since the mid-1990s. With six nations sharing the catchment, and over 60 million people living within it, the Mekong basin is now globally one of the most contested transboundary environmental commons.