The Great Ouse /ˈuːz/ is a river in the United Kingdom, the largest and longest of several British rivers called "Ouse". From Syresham in central England, the Great Ouse flows into East Anglia before entering the Wash, a bay of the North Sea. With a course of 143 miles (230 km), mostly flowing north and east, it is the fourth-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.