Ullswater, lake, 71/2 mi (12.1 km) long, Cumbria, NW England; second largest in the country. It is divided into three reaches. The waterfall of Aira Force (65 ft/20 m high) and Helvellyn Mt. are nearby. Gowbarrow, west of the lake, is said to have been the inspiration of William Wordsworth's poem "Daffodils."