Wales has both international and local rivers. The longest river in Wales is the River Severn, which has a length of about 354 kilometers. River Wye is second with a length of about 217 kilometers while Teme River is third with about 130 kilometers. ... Longest Rivers in Wales. RankRiverLength (km) 2Wye217 3Teme130 4Dee113 5Towy121 4 more rows 21 Dec 2020