Pen-y-Garreg Dam, Elan Valley, is on the middle level of the Elan Valley Water Scheme (nprn 96459). It retains Pen-y-garreg Reservoir (nprn 309537). Construction was completed in 1904. The engineer was James Mansergh. Total capacity: 6,055 megalitres; Top water level above OS Datum: 288m; Height of dam above river bed: 37m; Length of dam: 161m.

B.A.Malaws, RCAHMW, 21 November 2003.