Loch Lomond is a freshwater Scottish loch which crosses the Highland Boundary Fault, often considered the boundary between the lowlands of Central Scotland and the Highlands. Traditionally forming part of the boundary between the counties of Stirlingshire and Dunbartonshire, Loch Lomond is split between the council areas of Stirling, Argyll and Bute and West Dunbartonshire. Its southern shores are about 23 kilometres northwest of the centre of Glasgow, Scotland's largest city. The Loch forms part of the Loch Lomond and The Trossachs National Park which was established in 2002.
Loch Lomond is 36.4 kilometres long and between 1 and 8 kilometres wide, with a surface area of 71 km². It is the largest lake in Great Britain by surface area; in the United Kingdom, it is surpassed only by Lough Neagh and Lough Erne in Northern Ireland. In the British Isles as a whole there are several larger loughs in the Republic of Ireland. The loch has a maximum depth of about 153 metres in the deeper northern portion, although the southern part of the loch rarely exceeds 30 metres in depth.