It originates high in the Yorkshire Dales and ends where it meets the River Wharfe.

[3] The river's source is at Washburn Head, just south of Stump Cross Caverns.

The lower three (Lindley Wood, Swinsty and Fewston) were built at the end of the 19th century, while the fourth, Thruscross, was delayed until the 1960s.

[5] Fewston and Swinsty reservoirs have a surface area of around 1.6 square kilometres (0.62 sq mi) and a combined length of 4.1 kilometres (2.5 mi); Thackray Beck and Spinksburn Beck are major tributaries flowing into these reservoirs.

The valley floor consists of solid Millstone Grit overlain with till drift.