Stour, river, Cambridgeshire, Suffolk, and Essex, eastern England; rising as a number of headstreams in south-eastern Cambridgeshire and flowing south-east and east, forming the border between Suffolk and Essex, to join the North Sea at Harwich. The Stour's length is 75 km (47 mi) of which 15 km (9.5 mi) is estuary, between Manningtree and Harwich; its drainage basin is about 1,800 sq km (700 sq mi). The countryside along its banks in Suffolk and Essex was made famous by the paintings of John Constable.