North of Foel Goch are the remains of a stone-built weir, aligned north to south, across the course of Nant Edno. The weir comprises a 45m-long, 7m-wide double drystone wall with a rubble fill, reinforced with a stone bank on the east side. A notch has been cut through the central section of the weir in order to decommission the reservoir which lay to the east until the mid 20th century. The weir and reservoir are depicted on the 1st Edition 6" Ordnanace Survey map of 1891 and subsequent editions, but are shown as drained on the 1953 Ordnance Survey map. M.Railton, NPA, 20th October 2010.