Nant Gwys
The Nant Gwys is a river flowing off the Black Mountain (Y Mynydd Du) in Powys, Wales. Its tributaries Gwys Fawr and the Gwys Fach flow south from Banwen Gwyn and Bwlch y Ddeuwynt respectively and join forces to form the Nant Gwys proper which then flows for about 5 km / 3 mi to its confluence with the Afon Twrch at Cwm-twrch-Uchaf.
The upper reaches of the river and its tributaries lie within the Brecon Beacons National Park (Parc Cenedlaethol Bannau Brycheiniog) and within Fforest Fawr Geopark.[1] The river is one of several which run down the southward directed dip-slopes of the Black Mountain (Y Mynydd Du) passing from the Millstone Grit outcrop onto the mudstones of the Carboniferous Coal Measures.[2]
The name translates from Welsh as 'sow stream', presumably in reference to the neighbouring Afon Twrch or 'boar river'.