Derwentwater, or Derwent Water, is a lake in the Lake District in North West England. It is in the unitary authority of Cumberland within the ceremonial county of Cumbria. It is the third largest lake by area, after Windermere and Ullswater. It has a length of 4.6 km, a maximum width of 1.91 km, and an area of 5.4 square kilometres. Its primary inflow and outflow is the River Derwent, which also flows through Bassenthwaite Lake before reaching the Irish Sea at Workington.
