The Duddon is a river of north-west England. It rises at a point above sea level near the Three Shire Stone at the highest point of Wrynose Pass . The river descends to the sea over a course of about before entering the Irish Sea at the Duddon Sands. For its entire length the Duddon forms the boundary between the historic counties of Lancashire and Cumberland. Since local government re-organisation in 1974 the Duddon has been in the county of Cumbria.