Looking across Llyn Clywedog from the Waun y Gadair viewpoint at the western end of the reservoir. The dam which retains the reservoir is the tallest concrete dam in the UK at 72m, and completed in 1967, its purpose to contain the waters of the River Severn in the winter, and maintain water flow in the summer. Llyn Clywedog is 6 miles long, and lies in the hills between Llanidloes and Staylittle. For walkers, there are several trails around the lake, and Glyndwr's Way runs along the dam and the southern shore. Stocked with trout, Clywedog is an established fishing water run by Llanidloes Angling Society. Clywedog Sailing Club look after water sports on the lake.