The River Great Ouse is a river in England, the longest of several British rivers called "Ouse". From Syresham in Northamptonshire, the Great Ouse flows through Buckinghamshire, Bedfordshire, Cambridgeshire and Norfolk to drain into the Wash and the North Sea near Kings Lynn. Authorities disagree both on the river's source and its length with one quoting 160 mi (260 km) and another 143 mi (230 km). Mostly flowing north and east, it is the fifth longest river in the United Kingdom. The Great Ouse has been historically important for commercial navigation, and for draining the low-lying region through which it flows; its best-known tributary is the Cam, which runs through Cambridge. Its lower course passes through drained wetlands and fens and has been extensively modified, or channelised, to relieve flooding and provide a better route for barge traffic. The unmodified river would have changed course regularly after floods.

Northamptonshire is a ceremonial county in the East Midlands of England. It is bordered by Leicestershire, Rutland and Lincolnshire to the north, Cambridgeshire to the east, Bedfordshire, Buckinghamshire, Oxfordshire to the south and Warwickshire to the west. Northampton is the largest settlement and the county town.