The earth dam at Bwlch-y-gle was built as a subsidiary to Clywedog Dam (nprn 305772) to block a minor valley for the creation of Llyn Clywedog or Clywedog Reservoir (nprn 309930). It stands 12.7m high and is 183m long.
B.A.Malaws, RCAHMW, 27 January 2004.