The Elan Valley is filled with strikingly beautiful countryside, split by imposing Victorian and Edwardian dams and the lakes they've created. In the late 19th century, dams were built on the River Elan (pronounced 'ellen'), west of Rhayader, mainly to provide a reliable water supply for Birmingham. During WWII, the earliest of the dams was used to perfect the 'bouncing bomb' used in the storied Dambusters raid on targets in Germany's Ruhr Valley. In 1952 a fourth, large dam was inaugurated on the tributary River Claerwen. Together their reservoirs now provide over 70 million gallons of water daily for Birmingham and parts of South and Mid-Wales.
The need to protect the 70-sq-mile watershed (called the Elan Valley Estate) has turned it and adjacent areas into an important wildlife-conservation area, and in 2015 it was awarded Dark Sky Park status. The dams and associated projects also produce some 3.9 megawatts of hydroelectric power.