Nant-y-moch Reservoir is situated in the Cambrian Mountains in northern Ceredigion, Wales. The reservoir which flooded a part of the valley of the River Rheidol and its headwaters derives its name from a stream, the Nant-y-moch (in English = the pigs stream,), which formerly flowed into the River Rheidol at this spot. The dam is about three miles north of the village of Ponterwyd. The reservoir forms part of the Cwm Rheidol hydroelectric power scheme and the headwaters of the reservoir include the source of the River Rheidol.