This document discusses research on the potential impacts of dams being built along the Mekong River in Southeast Asia. It finds that the construction of 11 mainstem dams could result in the loss of 340,000 tonnes of fish, representing a 16% reduction in fish protein for the region. Replacing this lost protein through other means, such as expanding livestock or crop production, would require significant increases in water and land use with impacts on food prices and vulnerability for the poor.