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 2,001 feet, confirming its status as a mountain. Bwlch y Ddeufaen separates Tal y Fan from the main Carneddau ridge, the closest summit on which is Carnedd y Ddelw. Pen y Castell is directly opposite to the south. 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.