Derwent Water (also spelled Derwentwater) is a lake in North West England’s Lake District in County Cumbria. It is the third largest lake in the area and is entirely located in the Allerdale district. Just south of the town of Keswick, it plays an important tourist role, as does the town, with hiking, climbing and water sports being the main activities on offer.
Derwent Water is fed by and drains onto the River Derwent. The river connects the lake to the nearby Bassenthwaite Lake. There is a theory that the two lakes once formed a whole.
The lake covers an area of approximately 5.2 km², is more than 4.5 kilometers long and reaches a width of 1.6 kilometers. The average depth is only 5.5 meters, the maximum depth is 22 meters. The lake is surrounded by a hilly area, with in many cases wooded slopes.
The lake has four islands, one of which is inhabited: Derwent Island, which houses an 18th-century house managed by the National Trust, but privately inhabited, open five days a year for the public.