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.
Pen y Fan mountain is used by the military as part of the selection process of the UK's Special Forces personnel. Three soldiers who died after collapsing in the field in July 2013 were believed to have been climbing the mountain (see "Fan Dance") while undergoing Special Air Service selection. The peak is a major objective in the Beacons Way, a long distance footpath which passes from east to west across the massif, and is open to all walkers. There is well made, evenly graded footpath from the Storey Arms on the A470, which is 1500 feet below, allowing for safe access during