Ullswater is the second-largest lake in the Lake District - about seven miles long, three-quarters of a mile wide, with a maximum depth of sixty-three metres - and one of the most strikingly shaped. It is a Z, or an elongated S, depending on how you describe it: three distinct reaches, each carved by a different Ice Age glacier, meeting at sharp bends that hide each reach from the next. From any one point on the lake you can see only one third of it. The surrounding hills give it its shape; the glaciers gave it its depth. The lake drains north into the River Eamont, which joins the Eden, which reaches the Solway Firth at Carlisle. For much of its length Ullswater used to mark the border between the historic counties of Cumberland and Westmorland; today, more prosaically, it sits within the unitary authority of Westmorland and Furness.

The name's origin is genuinely uncertain. The leading scholarly guess is that it derives from Ulfr, an Old Norse personal name (also the noun for wolf), plus the Old English waeter influenced by the Norse vatn - giving "Ulf's lake." Several historical figures named Ulf have been proposed: a Norse chief who supposedly ruled the area, a Saxon Lord of Greystoke called Ulphus whose land bordered the lake. Other theories invoke the Norse god Ullr, or a Celtic word ulle meaning elbow - which would describe the lake's bent shape rather well. There is even a 19th-century theory that the lake was once a haunt of wolves. The truth is probably long lost. Hodgson Hill, an earthwork on the northeast shore, may be the remains of a Viking fortified settlement; the area was certainly settled by Scandinavian incomers. Whoever Ulf was, his name has outlived him by at least eleven hundred years.

The Ullswater Steamers fleet still runs all year. The boats were originally working vessels, from the 1850s carrying mail and miners and goods along the lake to and from the Greenside lead mine at Glenridding. When the mine closed in 1962, the steamers reinvented themselves as tourist craft. The oldest of the fleet, the Lady of the Lake, has been in service since 1877. In 1912 the lake had an unexpected royal visitor: Kaiser Wilhelm II, German Emperor, toured Ullswater on the MY Raven, temporarily re-fitted as a royal yacht for the occasion. The local landowner, Hugh Lowther, the 5th Earl of Lonsdale, built him a shooting lodge at Martindale. Two years later the Kaiser would be at war with Britain. The lodge, called The Bungalow, still stands. The connection at Pooley Bridge is older and arguably more honourable: Thomas Clarkson, who lived at Eusemere from 1796 to 1804, was one of the central figures in the campaign to abolish the British slave trade. He spent years travelling the country collecting evidence, addressing audiences, and helping William Wilberforce build the political case in Parliament. The lake gave him a view, a refuge, and friends who walked over from Grasmere to visit.

On 23 July 1955, the British speed-record pursuer Donald Campbell drove a jet-propelled hydroplane called Bluebird K7 down the calm waters of Ullswater at 202.32 mph, setting a new world water speed record. The lake was chosen for its length, its straightness through the central reach, and its sheltered surface. Campbell would go on to break further records on other lakes - Coniston in particular - until he was killed there in 1967 attempting to push past 300 mph. Bluebird K7 itself was eventually raised from Coniston in 2001, restored over two decades, and returned to Coniston Water in May 2026 — running under her own power for the first time since the day Campbell died. Ullswater hosts no jet-powered hydroplanes today. The lake is a sailing and rowing centre: the Ullswater Yacht Club runs the Lord Birkett Memorial Trophy, a two-day round-the-lake regatta held every July, that regularly attracts more than two hundred boats. The trophy commemorates the lawyer who, in 1962, gave his final speech in the House of Lords campaigning against a proposal to turn Ullswater into a reservoir. He won the vote. He died the next day. The lake remains a lake.

Midway along the western shore the Aira Beck falls down a wooded ravine in a series of cascades known as Aira Force. The National Trust owns the falls and the surrounding land. The path through the gorge is short, atmospheric, and remarkably loud after rain. Nearby Lyulph's Tower is a castellated 18th-century pele-tower lookalike, built by a former Duke of Norfolk as a shooting box - an architectural folly with the bones of a fortification. In 2022 the lake's resident greylag geese began disappearing in disturbing ways - witnesses on several occasions saw birds dragged under the water. Theories were aired: a very large pike, an introduced wels catfish, an otter, fishing-line entanglement. Nobody is sure. The geese continue to live on the lake, watchful. Wordsworth, who knew this lake well, called it "perhaps, upon the whole, the happiest combination of beauty and grandeur which any of the Lakes affords." From the western shore on a still spring day, with the daffodils still blooming and the Helvellyn range across the water, you would struggle to make a case against him.