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 Ogmore as Bridgend with concrete flood protection walls. The River Llynfi ("Afon Llynfi" in Welsh), runs for around 10 miles from its source north of Maesteg and flows generally southwards through the Llynfi Valley to the confluence with the River Ogmore at Aberkenfig. The River Garw flows broadly north-south and runs through Pontycymer to its confluence with the Ogmore (Ogwr) at Brynmenyn. The Ewenny River () rises to the north-east of Bridgend town and flows through Pencoed and Coychurch before entering the River Ogmore estuary just below Ogmore Castle. The industrialisation of the valley of the Ogmore by mining and heavy