Derwentwater is one of the principal bodies of water in the Lake District National Park in north west England. It is both fed and drained by the River Derwent. It measures approximately 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 within 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 a place of considerable scenic value. It is surrounded by hills (known locally as fells), and many of the slopes facing Derwentwater are extensively wooded. A regular passenger launch operates on the lake, taking passengers between various landing stages. There are seven lakeside marinas. The lake is believed to be the last remaining native habitat of the vendace (Coregonus vandesius) fish from the 4 originally known sites: Bassenthwaite Lake and Derwent Water in the Lake District and the Castle Loch & Mill Loch in Lochmaben.