It lies at the foot of Fan Brycheiniog,[2] the highest peak of the Black Mountain (Y Mynydd Du) range within the Brecon Beacons National Park.

[4] Shoreweed and quillwort are found here whilst greater water-moss occurs on boulders at the water's edge.

"[5] The surface of Llyn y Fan Fawr lies at about 1815 feet or 605m above sea level.

[8] Much of the land around the lake is peaty and thus wet underfoot.

The main route of the Beacons Way runs along the ridge above the lake whilst its low-level alternative wraps around the lake's eastern margin.