The River Severn is the longest river in Great Britain, spanning a total length of 220 miles (354 km). It originates in the Cambrian Mountains of mid-Wales at an altitude of 610 m (2,000 ft) on the Plynlimon massif, located near the Ceredigion and Powys borders.
The river flows through the counties of Shropshire, Worcestershire, and Gloucestershire, passing through the county towns of Shrewsbury, Worcester, and Gloucester. It is characterized by having the most voluminous flow of water in England and Wales, with an average flow rate of 107 m3/s (3,800 cu ft/s) at Apperley, Gloucestershire.