Aira Force is a waterfall in the English Lake District, in the county of Cumbria. The word force, from Old Norse fors, is used in many parts of northern England as a synonym for waterfall.
The stream which flows over the waterfall is Aira Beck, which rises on the upper slopes of Stybarrow Dodd at a height of 720 metres (2,362 ft) and flows north-easterly before turning south, blocked by the high heather-covered slopes of Gowbarrow Fell. It turns south on its eight-kilometre journey to join Ullswater, at a height of 150 metres (492 ft). One kilometre before entering the lake, the beck makes the 20 metres (66 ft) leap down a rocky ravine at the falls known as Aira Force.