Hydropower is booming on the Mekong River. The energy and money these dams produce are vital to a fast growing, rapidly developing region. The likely benefits of hydropower are substantial, but critics say many, if not most, of these large dams are going forward without a full reckoning of their environmental and social costs. There are more than 120 major hydropower dams planned along the Mekong and its major tributaries. We visited villages in the shadow of just one: the Lower Sesan2, planned near the confluence of Cambodia's Sesan and Srepok Rivers.