Clywedog Reservoir
Llanidloes Without, United Kingdom
The Clywedog Reservoir (Llyn Clywedog) is a reservoir near Llanidloes, Wales on the head-waters of the River Severn. The construction of the reservoir was enabled by an act of Parliament, the Clywedog Reservoir Joint Authority Act 1963 (c. xxxi), which asserted that "At certain times the flow of water in the river is inadequate... unless that flow were regulated so as to ensure that at those times water in addition to the natural flow will flow down the river."
Reservoir data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).