 Nearby is one of the few natural lakes in the park, the small Llyn Cwm Llwch.It may be compared with the much larger glacial lakes of Llyn y Fan Fach and Llyn y Fan Fawr below the main ridge of the Black Mountain about 15 miles west of the central Brecon Beacons escarpment.All three are glacial lakes and were formed during the last ice age by ice scouring out hollows below the peaks, the water being partly dammed by moraines of rock debris carried down by ice action subsequent to plucking and frost shattering.