To the west long and gentle slopes run down from the summit of Dow Crag toward the Duddon, while further north on this flank is Seathwaite Tarn. The ground here also begins in a shallow descent, but turns steep above the tarn in a line of minor crags. Seathwaite Tarn is a reservoir in a side valley of the Duddon system. This was originally a much smaller waterbody, but was dammed early in the 20th century to provide drinking water for the Barrow in Furness area. The dam is almost 400 yards long and is concrete cored with slate buttresses, the resulting depth being around 80 ft. Water is not abstracted directly from the tarn, but flows some distance downriver to an off-take weir.