It flows north through Buttermere and then Crummock Water, through Lorton Vale, to the town of Cockermouth, where it joins the River Derwent.

The river takes its name from the Brythonic Celtic word kukrā, meaning 'the crooked one.

The small river came to national prominence in the 2009 Great Britain and Ireland floods.

The county of Cumbria was the hardest hit area during the floods, when the River Cocker and River Derwent both burst their banks, covering the town of Cockermouth in as much as 8 feet (2.4 m) of water, causing extensive damage to houses, shops, workplaces as well as the home of Cockermouth Cricket Club.

[2] An important and pioneering project to reduce the flooding hazards associated with the river Cocker began in 2014.