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. In total, from source to the westernmost part of Duddon Sands, its length is . For its entire length the Duddon forms the boundary between the historic counties of Lancashire and Cumberland and since local government re-organisation in 1974 the Duddon has been in the ceremonial county of Cumbria. The catchment area of the River Duddon includes a substantial part of the south-western Lake District fells, including the eastern slopes of Corney Fell, Ulpha Fell and Harter Fell; the southern slopes of the mountains around the head of Langdale, and the western slopes of Dunnerdale and Seathwaite Fells. From its source the Duddon falls rapidly over a distance of two miles (3.2 km) to Cockley Beck at the head of Dunnerdale. Close to the hamlet of Seathwaite the Tarn Beck from Seathwaite Tarn is subsumed. The river then takes a south-westerly direction to Ulpha Bridge. Passing under the Duddon Valley road, the river assumes a southerly course to Duddon Bridge where it is crossed by the A595 trunk road. After about a mile (1.6 km) the Duddon becomes tidal as it opens into the Duddon Estuary between Furness and south-west Cumberland. Literary associations The River Duddon and the Duddon Estuary have figured prominently in the work of the Cumbrian poet Norman Nicholson, who said of the river valley that “Without hesitation this is my favourite place of all. There is such variety, such texture”. Arthur Ransome figured the valley under the name ‘Dundale’ in his Lake novels. The poet William Wordsworth wrote extensively of the Duddon, a river he knew and loved from his early years. He wrote his lyric sequence "The River Duddon, A Series of Sonnets" between 1804 and 1820. This sequence first appeared in The River Duddon, A Series of Sonnets: Vaudracour and Julia: And Other Poems. To which is annexed a Topographical Description of the Country of the Lakes in the North of England in April 1820, and later in Wordsworth's Miscellaneous Poems in July 1820. (Although it was first published as a series of 33 sonnets, the Duddon series was expanded to 34 sonnets in the