The Adur (/eɪˈdʊər/ or /eɪˈdɜː/) is a river in Sussex, England; it gives its name to the Adur district of West Sussex. The river, which is 20 miles (32 km) long, was once navigable for large vessels up as far as Steyning, where there was a large Saxon port, but by the 11th century the lower river became silted up and the port moved down to the deeper waters at the mouth of the river in Shoreham-by-Sea.