The River Usk (/ʌsk/; Welsh: Afon Wysg) 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. The Monmouthshire and Brecon Canal follows the Usk for most of the length of the canal.