Dinorwig is a 1320 MW pumped storage hydroelectricity scheme in the Pass of Llanberis on the edge of the Snowdonia national park in north Wales. It is comprised of 16 km of tunnels, 1 million tons of concrete, 200,000 tons of cement and 4,500 tons of steel, housed beneath the mountain Elidir Fawr.

The scheme was constructed in an the abandoned Dinorwig slate quarry. Water is stored at high level in Marchllyn Mawr and is discharged into Llyn Peris . Excess water overflows to Llyn Padarn and is lost to the system. Both Llyn Peris and Llyn Padarn were ancestral homes to the Arctic char, a rare fish in the UK. When the scheme was commissioned, a fish rescue was undertaken to transfer the char from Llyn Peris to other local suitable lakes and it is believed that due to the very variable water levels in Llyn Peris, Arctic char are now absent from the lake.