The Mahaweli River diversion project in Sri Lanka included the construction of a cascade of large dams along river Mahaweli, which drains one sixth of the country. The reservoirs inundated many ancient villages in Central Hill areas. This paper describes the Mahaweli project with special emphasis on Upper Mahaweli and looks at the fate of the migrant families 20 years after they left, with the inundation of their traditional lands. This discussion is an attempt to follow the good examples, and to avoid repeating the mistakes if any.