The River Arun flows through West Sussex in southern England, running from its upper reaches near Horsham and Billingshurst southward through Pulborough, Amberley, Arundel, and out to the sea at Littlehampton. It is reputedly the second fastest-flowing river in England, and its lower sections are tidal, a factor that significantly shapes the paddling experience throughout much of the river's length.

The tidal influence extends well inland. High tide at Pulborough occurs approximately four hours after high tide at the river's mouth at Littlehampton, while Amberley sees high tide roughly two hours after Littlehampton. Tidal constants relative to Dover have been recorded as follows: river entrance +0:10, Littlehampton Wharf +0:15, Arundel +1:20, Offham +1:40, Amberley +2:40, Greatham +3:25, and Pulborough +4:10. Paddlers should account for rainfall and atmospheric pressure when using these figures. Downstream of Bury, the speed of the current increases and demands greater fast-water experience.

A popular route runs from the Black Rabbit pub at Offham near Arundel upstream to Amberley Bridge, a distance of approximately 4.5 miles one way. The return trip, aided by the tide throughout, takes around three hours at a relaxed pace. The recommended approach is to depart from Offham at the time of high tide at Littlehampton. There was previously a tearoom at Amberley where paddlers could land, though landing fees and access restrictions have changed over time.

The middle section between Pulborough and Amberley offers paddling through water meadows backed by the South Downs. Upstream from Pulborough toward Pallingham Quay, the river narrows and becomes more overgrown, with tree blockages and limited access making it a more challenging and less frequently paddled stretch. The upper section from Stopham Bridge near Pulborough to Pallingham Quay is offered as a guided trip suitable for beginners and experienced paddlers alike.

At Pulborough, a public slipway at the old Swan Bridge provides free access to the river. At Littlehampton, the public slipway near the RNLI station leads directly into the river, though harbour dues apply. The Littlehampton slipway is best used within two hours either side of high tide to avoid mud. Wildlife along the river includes kingfishers, dragonflies, and swans. Kayak, canoe, and paddleboard hire is available at Pulborough through local operators.