This small lake is on the ridge which runs from Y Gamriw to Drygarn Fawr in the Cambrians, high above Caban Coch Reservoir in the Elan Valley. Together with the huge peat bog of Cnapiau'r Ferlen, it is the source of the River Chwefri, a 12 mile long tributary of the River Irfon which it meets on the edge of Builth Wells.