Mid C20 concrete dam built across Nant y Calch and Nant y Gawrnant. Approximately 50m N-S, 3m deep on the reservoir side (which was dry at the time of survey), raked downhill side, and central narrow spillway with concrete-lined channel below it. Probably provided water to Maerdy No 3 pit (nprn 33505).
Recorded as part of Uplands Initiative Survey. R Hayman, H&H, 06/10/2009.