The River Cocker is a river in the Lake District in North West England, in the county of Cumbria. Its source is at the head of the Buttermere valley. It flows north through Buttermere and then Crummock Water, through Lorton Vale, to the town of Cockermouth, where it joins the River Derwent. It is roughly 12 miles long. The river takes its name from the Brythonic Celtic word kukra, meaning 'the crooked one.' The river supports a range of wildlife; the predominant fish species include salmon, sea trout, brown trout, eels, minnows, sticklebacks and the Stone Loach.