The Greater Mekong Subregion (GMS) has been styled as a natural region drawn together by the Mekong River. However, the literature on regional identity has argued that regions are socially constructed phenomena. River basins in particular are historically evolveed constructs of specific political and social relations. Drawing on concepts of regional identity and on the literature examining the links between culture and water, the article argues that the actors driving the GMS have exacerbated social tensions through hydropower programmes, thus failing to establish social coherence. These programmes focus on energy production for national economic growth and economic integration between GMS countries, but they ignore the need to govern water resources for the benefit of local communities, many of which are made up of ethnic minorities with specific cultural attachments to the river. This produces tensions around the type of development that takes place in the GMS, leading to value fragmentation rather than value convergence. The article explores these issues by focusing on the Chinese-built Lower Sesan 2 Dam in Cambodia.