Llyn Stwlan was a small, corrie lake until the late 1950s when the dam was built as part of the Ffestiniog Hydro-Electric pumped storage scheme. Lying 1500 feet above sea level in the Moelwyn mountains, Stwlan is the top reservoir from which the water drops 1000 feet to turn turbines at the Ffestiniog Power Station. The water is held in a lower reservoir before being pumped back to Stwlan when the demand for electricity is low. Footpaths and a road (closed to cars) lead to Llyn Stwlan from Tanygrisiau, where there are car parks.
