Cantref Reservoir dam, including valve house, draw-off tower and spillway, (partly in Llanfrynach)

The Cantref Reservoir dam, which includes a valve house, draw-off tower, and spillway, is a Grade II listed structure. The dam features a clay core and earth bund construction, with a pitched stone inner face that ends in a battered rock-faced masonry wave-wall topped with simple cast-iron railings. The outer face is turfed.

On the east side of the dam, there is a single-storey draw-off tower made of coursed rock-faced stone. It has a flat roof that is concealed behind a parapet. The tower includes a round-headed doorway with replacement doors and a metal plaque in the tympanum that commemorates the opening of the reservoir in 1892. Above the doorway is a moulded cornice, and there is a single window at the rear, which has been renewed in its original round-headed opening.

At the west end of the dam, a spillway is present, marked by a short pier with a rounded end made of rock-faced stone facing the reservoir, and dressed stone leading to the spillway. A segmentally-arched bridge crosses the spillway at the dam's end. The spillway consists of a stone-paved channel with dressed stone revetment on the west bank, below a rock-faced dwarf wall with railings and a gateway. The channel continues downstream with a series of weirs featuring stepped and ramped dressed stone revetments topped with free-stone copings. An auxiliary siphon spillway was added in the later 20th century.