|Primary inflows||River Derwent, Watendlath Beck, Brockle Beck|
|Primary outflows||River Derwent|
|Max. length||4.6 kilometres (2.9 mi)|
|Max. width||1.91 kilometres (1.19 mi)|
|Surface area||2 sq mi (5.2 km2)|
|Average depth||5.5 m (18 ft)|
|Max. depth||22 m (72 ft)|
|Water volume||29 x 106 m³|
|Residence time||55 days|
|Shore length1||9.6 mi (15.4 km)|
|Surface elevation||75 metres (246 ft)|
|Islands||4 plus 9 small (13)|
|1 Shore length is not a well-defined measure.|
The lake lies immediately south of the town of Keswick. It is both fed and drained by the River Derwent. It is about 3 miles (4.8 km) long by 1 mile (1.6 km) wide and is some 72 feet (22 m) deep. There are several islands in the lake, one of which is inhabited. Derwent Island House, an 18th-century residence, is a tenanted National Trust property open to the public on five days each year.
Derwentwater is very scenic. It is surrounded by hills (known locally as fells), and many of the slopes facing Derwentwater are wooded. A regular passenger launch operates on the lake, taking passengers between various landing stages. There are seven lakeside marinas, the most popular stops being: Keswick, Portinscale and the Lodore Falls, from which boats may be hired. Recreational walking is a major tourist activity in the area and there is a network of footpaths in the hills and woods surrounding the lake.
The Keswick—Borrowdale road runs along the eastern shore of the lake and carries a regular bus service. There is a lesser road along the western shore connecting the villages of Grange and Portinscale.
Derwentwater gave its name to the Earldom of Derwentwater.