Ystradfellte Reservoir is a water storage reservoir on the Afon Dringarth in the upland area of Fforest Fawr within the Brecon Beacons National Park in South Wales.

It lies just north of the village of Ystradfellte in the county of Powys at OS Grid ref SN 946178.

The reservoir was constructed between 1907 and 1914 by Neath Rural District Council for the supply of water.

A temporary railway track was constructed for 7 miles (11 km) from the village of Penderyn to transport building materials to the dam site.

Limestone was obtained from Penderyn Quarry and puddle clay was excavated from the glacial till at nearby Cilhepste Coed.