    the arun () is a river in the english county of west sussex. its source is a series of small streams in the st leonard's forest area, to the east of horsham. after flowing through horsham to the west, it is joined by the north river at nowhurst. turning to the south, it is joined by its main tributary, the western river rother, and continues through arundel and past arundel castle, to join the english channel at littlehampton. the arun local government district in west sussex is named after it. it is one of the faster flowing rivers in england, and is tidal as far inland as pallingham quay,  upstream from the sea at littlehampton. the first major improvements to the river were made between the 1540s and the 1570s, when arundel became a port, and navigation up to pallingham was improved, but barges had difficulty negotiating the [[flash 
Ramsar_sites_in_England River_navigations_in_the_United_Kingdom Rivers_of_Sussex