From its source at
AMSL on the upper slopes of Bryn Garw in the
Cambrian Mountains the Irfon flows southwards past the foot of the Devil's Staircase, along the Abergwesyn Valley, through the scenic Camddwr Bleiddiad (Wolves' Gorge), and into the Wolves' Pool. It then flows past a forest of
sessile oak (Quercus petraea) to join the Afon Gwesyn at Abergwyesn where it passes beneath the Irfon Forest and the Nant Irfon National Nature Reserve towards Llanwrtyd Wells. Lastly, overlooked by the scarp of
Mynydd Epynt to the south, it flows eastward through
Llangammarch Wells, and
Garth to join the
River Wye at Builth Wells (Llanfair ym Muallt) approximately 28 winding miles from its source. The name 'Irfon' may be identical in its origin to the
River Irvine in Scotland, for which
multiple etymologies have been proposed. ==History==