Upper Arun is a 17.6-hectare (43-acre) biological Site of Special Scientific Interest between Billingshurst and Pulborough in West Sussex.

This 13-kilometre (8-mile) long stretch of the River Arun provides the habitat for a rich riverine flora, such as common club-rush and reed canary-grass. It is an outstanding site for breeding dragonflies, including the clubtail, hairy, brilliant emerald and the nationally rare scarce chaser.

50°59′17″N 0°30′50″W / 50.988°N 0.514°W / 50.988; -0.514