Coedty Reservoir is a reservoir in Snowdonia, North Wales. It is fed by the waters of Afon Porth-llwyd which flows from Llyn Eigiau. The reservoir lies at a height of 900 feet (274 m), and measures some 12 acres (49,000 m2) in size. It contains brown trout. The original dam was built in 1924 to provide hydro-electric power to the aluminium smelting works in Dolgarrog. In 1925, the Eigiau dam broke, and the flood of water from that also burst Coedty dam. The resultant flood caused the loss of 17 lives in Dolgarrog. The dam was rebuilt in 1926, and altered again in 1956.