It begins at the confluence of the Brennand River and Whitendale River, both of which rise high up in the surrounding moorland. It then flows through the steep-sided Dunsop Valley before meeting the Hodder. The Thirlmere Aqueduct, which carries water from the Lake District to Manchester, runs alongside.
On 8 August 1967 Dunsop Valley entered the UK Weather Records with the Highest 90-min totalrainfall at 117 mm. As of July 2006 this record remains.