River Usk River Usk The River Usk (; ) rises on the northern slopes of the Black Mountain ("y Mynydd Du"), Wales, in the westernmost part of the Brecon Beacons National Park. Initially forming the boundary between Carmarthenshire and Powys, it flows north into Usk Reservoir, then east by Sennybridge to Brecon before turning southeast to flow by Talybont-on-Usk, Crickhowell and Abergavenny after which it takes a more southerly course. Beyond the eponymous town of Usk it passes the Roman legionary fortress of Caerleon to flow through the heart of the city of Newport and into the Severn estuary at Uskmouth beyond
River Severn at Tewkesbury, Gloucestershire. The port of Bristol is on the Severn Estuary, where another River Avon flows into it through the Avon Gorge. The River Wye, from its source in Plynlimon, Wales ( from the source of the Severn), flows generally south east through the Welsh towns of Rhayader and Builth Wells. It enters Herefordshire, flows through Hereford, and is shortly afterwards joined by the River Lugg, before flowing through Ross-on-Wye and Monmouth, and then southwards where it forms part of the boundary between England (Forest of Dean) and Wales. It flows into the Severn near the town of Chepstow,