The River Granta is the name of two of the four tributaries of the River Cam, although both names are often used synonymously. The Granta, starts near the village of Widdington in Essex flowing north past Audley End House to merge with the other contributary Rhee, which is also commonly called River Cam, a mile south of Grantchester. From source to its confluence with the Rhee it is 41.7 kilometres (25.9 mi) in length.
A further tributary, also known as the Granta, runs 10 mi (16 km) from south of Haverhill to join the larger Granta south of Great Shelford. Another minor tributary is Bourn Brook which has its source near the village of Eltisley, 10 mi (16 km) west of Cambridge, running east through Caxton, Bourn and Toft to join the Cam at Byron's Pool.
In many maps the river changes its name at the Silver Street Bridge in Cambridge and is called "Granta" above and "Cam" below it.
In earlier times even the lower part of the Cam was also named the Granta, but after the name of the Anglo-Saxon town of Grantebrycge had been modified to Cambridge, the river was renamed to match.
- Franz X. Bogner & Stephen P. Tomkins: The Cam. An Aerial Portrait of the Cambridge River. Laber Foundation, 2015. ISBN 978-0-9932642-0-7 (http://www.cambridgeriver.info/).