The River Twiss is a river in the county of Yorkshire, England. The source of the river is Kingsdale Beck which rises at Kingsdale Head at the confluence of Back Gill and Long Gill in the Yorkshire Dales. Beneath Keld Head, it changes its name to the River Twiss. It has two notable waterfalls, Thornton Force and Pecca Falls, and its course follows part of the Ingleton Waterfalls Walk, then through Swilla Glen to Thornton in Lonsdale and down to Ingleton, where it meets the River Doe to form the River Greta.