Many of the drains or lodes leading off the river have been navigable since Roman times. In the Middle Ages, the river was used to transport stone to the university and corn dowstream to the Great Ouse and onwards to Kings Lynn. As the university expanded, the river was needed for the transport of food and building materials. In 1703, an Act was passed for improvements above Clayhithe, and a further Act in 1813.
The Cam Conservators have been navigation authority for the river above Bottisham Lock since 1703. Navigation above Jesus Green Lock, through 'The Backs' is usually by arrangement only, this part of the river usually being the preserve of punts in the summer months, and often very busy.
There is a detailed history at Wikipedia.