Ouse, Great

River that rises near Brackley in Northamptonshire, central England, and flows eastwards through Buckinghamshire, Bedfordshire, Cambridgeshire, and Norfolk, before entering the Wash north of King's Lynn; length 250 km/160 mi. A large sluice across the Great Ouse, near King's Lynn, was built as part of extensive flood-control works in 1959.

The chief tributaries of the Great Ouse are the Ivel, Cam, Lark, Little Ouse, Wissey, and Nar, all of which come from the south or east. The Bedfordshire Ouse was diverted in the 17th century from its devious course through Ely via two new channels called the New and Old Bedford rivers, 32 km/20 mi long, running in a direct line from Earith near St Ives to Denver Sluice near Downham Market.