Loch Ness is a large, deep, freshwater loch in the Scottish Highlands extending for approximately 23 miles (37 km) southwest of Inverness. Its surface is 52 ft (16 m) above sea level. Loch Ness is best known for alleged sightings of the cryptozoological Loch Ness Monster, also known affectionately as "Nessie". It is connected at the southern end by the River Oich and a section of the Caledonian Canal to Loch Oich. At the northern end there is the Bona Narrows which opens out into Loch Dochfour, which feeds the River Ness and a further section of canal to Inverness. It is one of a series of interconnected, murky bodies of water in Scotland; its water visibility is exceptionally low due to a high peat content in the surrounding soil.

Loch Ness is the second largest Scottish loch by surface area at 22 sq mi (56 km2) after Loch Lomond, but due to its great depth, it is the largest by volume. Its deepest point is 755 ft (230 m), making it the second deepest loch in Scotland after Loch Morar. It contains more fresh water than all the lakes in England and Wales combined, and is the largest body of water on the Great Glen Fault, which runs from Inverness in the north to Fort William in the south.

Loch Ness is the alleged 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 has varied since it was first brought to the world's attention in 1933.