Loch Ness, long, narrow lake, northern Scotland, forming part of the Caledonian Canal. It extends in a northeastern direction for 37 km (23 mi) from Fort Augustus to a point near the city of Inverness. The average width of the lake is about 2 km (about 1 mi), and the greatest depth is about 230 m (about 754 ft). It is drained by the Ness River into Moray Firth. The lake is reportedly the home of the so-called Loch Ness monster, but its existence has never been proven.