The Duddon is a river of north-west England. It rises at a point 1,289 feet (393 m) above sea level near the Three Shire Stone at the highest point of Wrynose Pass (grid reference NY277028). The river descends to the sea over a course of about 15 miles (24 km) 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.