The Arun rises 120 metres above sea level at its source in St Leonard's Forest near Horsham. It then runs 25 miles before reaching the sea at Littlehampton.
It's the second fastest flowing river in England with a 'flashy' nature responsive to heavy rainfall.
The river is tidal as far inland as Pallingham Quay, 18.25 miles upstream from Littlehampton.
See other images of River Arun