The Severn (known as Afon Hafren in Wales) is the longest British river, at 354 kilometres/210 miles long; it rises at an altitude of 610 metres on Plynlimon near Llanidloes, Wales, and it passes through a number of British counties, with the county towns of Worcester, Gloucester and Shrewsbury located on its banks.
The two Severn Bridges (opened in 1966 and 1996) link Wales with the southern counties of England and are among the most important in Britain. The Severn is bridged at many places, and many of these bridges are notable in their own right, with several designed and built by the engineer Thomas Telford. (See List of Severn bridges for more).
A six mile stretch of the Severn valley in Shropshire, known as the Ironbridge Gorge, was designated a World Heritage Site by UNESCO in 1986. Its historic importance is due to its role as the centre of the iron industry in the early stages of Britain's Industrial Revolution. Ironbridge gets its name from the bridge across the Severn, built in 1779 which was the first cast iron bridge ever constructed.
According to some sources, the name "Severn" is derived from the name Sabrina (or "Sabern"), based on the mythical story of the drowning of a nymph in the river.
The Staffordshire & Worcestershire Canal, the Worcester & Birmingham Canal, the Droitwich Canals and the Herefordshire & Gloucestershire canal are joined to the Severn.
A curious phenomenon associated with the lower reaches of the Severn is the tidal phenomenon known as the Severn bore. The river's estuary, part of the Bristol Channel, has the second largest tidal range in the world - about 15 metres - and at certain combinations of the tides, the rising water is funneled up the estuary into a wave that travels rapidly upstream against the river current; enthusiasts even attempt to surf along on the wave. The Severn Bore is a natural example of a self-reinforcing solitary wave or soliton.