The River Teifi (Welsh: Afon Teifi) forms the boundary between the counties of Ceredigion and Carmarthenshire in south-west Wales for most of its length, and the boundary between Ceredigion and Pembrokeshire for the final 3 miles (5 km) of its total length of 76 miles (122 km) (making it the longest river wholly in Wales), flowing into the sea below the town of Cardigan.