What is the largest lake by volume in the British Isles?

Loch Ness is a large, deep, freshwater loch in the Scottish Highlands extending for approximately 37 kilometres (23 miles) southwest of Inverness. At 56 km2 (22 sq mi), Loch Ness is the second-largest Scottish loch by surface area after Loch Lomond, but due to its great depth, it is the largest by volume in the British Isles. Its deepest point is 230 metres (126 fathoms; 755 feet), making it the second deepest loch in Scotland after Loch Morar. A 2016 survey claimed to have discovered a crevice extending to a depth of 271 m (889 ft), but further research determined this to be a sonar anomaly. It contains more water than all the lakes in England and Wales combined, and is the largest body of water in the Great Glen, which runs from Inverness in the north to Fort William in the south.

Loch Ness is known as the home of the Loch Ness Monster (also known as "Nessie"), a cryptid, reputedly a large unknown animal. It is similar to other supposed lake monsters in Scotland and elsewhere, though its description varies from one account to the next. Popular interest and belief in the animal's existence have varied since it was first brought to the world's attention in 1933.

Loch Ness is named for the river Ness which flows from the loch's northern end. The river's name probably derives from an old Celtic word meaning "roaring one".

Lough Neagh is the largest lake by area in the British Isles.