The River Stour is a river in East Anglia, England. It is 76 km (47 m) long and forms most of the county boundary between Suffolk to the north, and Essex to the south. It rises in eastern Cambridgeshire, passes though Haverhill, Cavendish, Sudbury and the Dedham Vale, and joins the North Sea at Harwich. The name Stour derives from the Celtic sturr meaning "strong".
The first settlement on the river in Suffolk was at Great Bradley, where man has had a recorded presence for over 5,000 years.
The River Stour was one of the first improved rivers or canals in England. Parliament passed 'An Act for making the River Stower navigable from the town of Manningtree, in the county of Essex, to the town of Sudbury, in the county of Suffolk' in 1705, mandating public navigation rights and providing the basis of a joint stock company of London and Suffolk investors who raised £4,800 to cut and manage the river. Although partly supplanted by railways, lighters were still working on the Stour almost until World War II.
The Stour valley has been portrayed as a working river by John Constable, Thomas Gainsborough and Paul Nash. Today much of the Stour valley is designated an Area of Outstanding Beauty. and forms the spine of Constable country.
The River Stour Trust, a waterway restoration group, was set up in 1968 to protect and enhance the right of the public to navigate the River Stour. The Trust seeks to restore through navigation from Sudbury to the sea, following on the successful restoration of the locks at Dedham, Flatford and Great Cornard, by reinstating the 10 remaining locks. Meanwhile, the Trust encourages use of the River Stour by small craft and organises annual events for all age groups and abilities on different parts of the river. River Stour Trust boat trips and private charters, skippered by friendly volunteer boat crew, are available in Flatford and Sudbury between Easter and October.