The reservoir and dam were constructed between 1911 and 1920 by Alexander Binnie, Son and Deacon (Resident Engineer John M. Parkin Assoc M.Inst.

The bulk of the reservoir lies in Cerrigydrudion community, while the northern arm forms the boundary between Pentrefoelas, to the west, and Llansannan and Nantglyn, to the north and east.

The "first stone" of the dam records that the engineers were Alex Binnie and George Deacon and the contractors were Sir Robert McAlpine.

However the reservoir has an extensive network of trails (public footpaths as well as forest roads suitable for horse riding, mountain biking and walking).

Footpaths around the reservoir were upgraded in 2005 and 2006, providing better access to the general public and allowing greater exploration of the North and South Alwen forests.