The River Avon () is in the south of England, rising in Wiltshire, flowing through that county's city of Salisbury and then west Hampshire, before reaching the English Channel through Christchurch Harbour in the Bournemouth, Christchurch and Poole conurbation of Dorset.
It is sometimes known as the Salisbury Avon or the Hampshire Avon to distinguish it from namesakes across Great Britain. It is one of the rivers in Britain in which the phenomenon of anchor ice has been observed. The Avon is thought to contain more species of fish than any other river in Britain. Long-farmed pastures and planted, arable fields line much of the valley; an indication of the wealth these brought to landowners is in ten large listed houses with statutorily recognised and protected parks. Many prehistoric sites and broader "landscapes" are found on either side of the river, the largest being the World Heritage Site zone of Stonehenge, Avebury and Associated Sites, followed by the Old Sarum knoll fortification and the Thornham Down prehistoric and medieval landscape.
Etymology
The river's name is a tautology: Avon is the Proto-Brythonic word meaning "river".
Course
The Avon begins as two separate bodies of water. The western arm rises to the east of Devizes, draining the Vale of Pewsey, and is joined by Etchilhampton Water which rises in the Bishops Cannings area and flows south past Etchilhampton and through Patney. The eastern arm rises at Easton Royal, east of Pewsey, and is joined by the Woodborough Stream which rises at Alton Priors and flows south through Woodborough and North Newnton.
The two branches merge at Upavon, flowing southwards across Salisbury Plain through Durrington, Amesbury and Salisbury. To the south of Salisbury the river enters the Hampshire Basin, flowing along the western edge of the New Forest through Fordingbridge and Ringwood, meeting up with the River Stour at Christchurch, to flow into Christchurch Harbour. The harbour opens into the English Channel past a cluster of small mouths of brooks from the New Forest and a broad sandbank, which is all built up as the Mudeford part of the harbour.
All the significant direct and indirect tributaries of the Avon, including the Nadder, Wylye, Bourne and Ebble, converge within a short distance around Salisbury.
A short distance north from the river's western source is Morgan's Hill, which marks the hydrological triple divide of Great Britain, where rainfall drains into the English Channel (via this River Avon), the Atlantic Ocean (via the Bristol Avon and Severn Estuary) and the North Sea (via the Kennet and Thames).
About half of the river is in Wiltshire; the rest is split between Hampshire and (since the 1974 boundary changes) Dorset.
As two Avons drain parts of Wiltshire, the river is popularly known as the Hampshire Avon or the Salisbury Avon (and the other as the Bristol Avon).
17th-century navigation
Construction of a navigation from Salisbury to Christchurch was authorised by the River Avon Navigation (Christchurch to New Sarum) Act 1664 (16 & 17 Cha. 2. c. 12). Work began in 1675 and the route was completed in 1684, but it fell out of use around 1715. Canalised channels were dug to straighten sections of the river, including one through Britford parish just below Salisbury; a lock survives on this section near Longford Castle, having been rebuilt in brick as a pound lock soon after the original flash lock was damaged by flooding in the early 18th century.
Path
The Avon Valley Path follows the river between Salisbury and Christchurch.