The River Cam is a tributary of the River Great Ouse in the east of England. The two rivers join to the south of Ely at a place called Pope's Corner. The Great Ouse connects the Cam to England's canal system.
The Cam connects Cambridge with the North Sea at King's Lynn, a total distance of about 40 miles (64 km). An organisation called the Conservators of the River Cam was formed in 1702, charged with keeping the river navigable. The Conservators are responsible for the three locks in and north east of Cambridge: Jesus Lock, Baits Bite Lock and Bottisham Lock. The stretch above Jesus Lock is known as the Top River, and passes to the Mill Pond and a weir to go upstream through Byron's Pool and the village of Grantchester where it is fed by many streams. The Top River is open only to punts and rowing boats. The stretch between Jesus Lock and the Mill Pond includes the Backs, which is the most popular section for tourists as it provides good views of several colleges. The stretch north of Baits Bite Lock is called the Lower River.
College rowing teams use the river between Jesus Lock and Bottisham Lock. There are many houseboats in Cambridge on the lower river and a few move onto the middle river during the winter.
In earlier times the Cam was named the Granta. After the name of the Anglo-Saxon town of Grantebrycge had been modified to Cambridge, the river was renamed to match.
The two principal tributaries of the Cam are known as the Granta and the Rhee, though both are also officially known as the Cam. The Rhee begins just west of Ashwell in Hertfordshire running 12 miles through the farmland of southern Cambridgeshire. The longer tributary, the Granta, starts near the village of Widdington in Essex flowing the 15 miles north past Audley End House to merge with the Rhee a mile south of Grantchester. A further tributary, also known as the Granta, runs 10 miles from south of Haverhill to join the larger Granta south of Great Shelford, home village of the children's author Philippa Pearce whose books (most notably Minnow on the Say) rename the River Cam as the River Say, with Great and Little Shelford becoming Great and Little Barley, and Cambridge becoming "Castleford" (not to be confused with the real town of the same name in West Yorkshire).
Another minor tributary is Bourn Brook which has its source near the village of Eltisley, 10 miles west of Cambridge, running east through Caxton, Bourn and Toft to join the Cam at Byron's Pool, where the famous poet is reputed to have swum.