At Harston it passes Harston Mill, the site of a water mill from at least the 11th century until the need for mill died out in the mid-20th century, and the parish church of All Saints.
The longer tributary, the Granta, starts in the parish of Debden to the east the village of Widdington in Essex.
Forming the boundary between Great Shelford and Little Shelford, it turns west to flow past Hauxton to merge with the Rhee a mile south of Grantchester at Hauxton Junction.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."The Reeve's Tale" from Geoffrey Chaucer's Canterbury Tales begins: Byron's Pool is named after the poet, Lord Byron, who is reputed to have swum there.In total, the Cam runs for around 69 kilometres (43 mi) from its furthest source (near Debden in Essex) to its confluence with the Great Ouse.) rather than the other way around: After the city's present name developed in Middle English, the river's name was backformed to match.