The River Severn is the longest river in Great Britain, with a length of 220 miles (354 km). It is also the river with the most voluminous flow of water by far in all of England and Wales. It rises in the Cambrian Mountains in mid Wales, at an altitude of 610 m (2,000 ft), on the Plynlimon massif, which lies close to the Ceredigion/Powys border near Llanidloes. The river then flows through Shropshire, Worcestershire and Gloucestershire. The county towns of Shrewsbury, Worcester and Gloucester lie on its course. By convention, the River Severn is usually considered to end, and the Severn Estuary to begin, after the Prince of Wales Bridge, between Severn Beach in South Gloucestershire and Sudbrook, Monmouthshire. The estuary discharges into the Bristol Channel, which opens into the Celtic Sea and from there into the Atlantic Ocean.
