Llyn y Fan Fawr outflow is to the River Tawe. Much of the land around the lake is peaty and thus wet underfoot. Llyn y Fan Fawr Llyn y Fan Fawr (Welsh: 'lake of the big peak') is a natural lake in the county of Powys, Wales. It lies at the foot of Fan Brycheiniog, the highest peak of the Black Mountain (Welsh"Y Mynydd Du") range within the Brecon Beacons National Park. Created as a result of glacial action, it is one of the largest glacial lakes in southern Wales. The lake is roughly rectangular in shape with its long axis oriented roughly north-south.
Tal y Fan Tal y Fan Tal y Fan is an outlying peak of the Carneddau mountains in North Wales. It is one of the four Marilyns that make up the Carneddau, the others being Carnedd Llywelyn, Pen Llithrig y Wrach and Creigiau Gleision. It is high, and lies midway between the Conwy valley to the east and Penmaenmawr on the coast to the north-west. It is the most northerly 2000 ft summit in Wales. On 6 May 2013 BBC News reported that a precise GPS measurement of Tal y Fan's height had been verified by the Ordnance Survey as 609.98 metres or