Loch Lomond is a freshwater loch lying on the Highland Boundary Fault, often considered the boundary between the lowlands of Central Scotland and the Highlands. It is 24 miles (39 km) long and between 3⁄4 and 5 miles (1.2–8.0 km) wide. It has an average depth of about 121 feet (37 m), and a maximum depth of about 620 feet (190 m). Its surface area is 27 sq mi (70 km2), and it has a volume of 0.62 cu mi (2.6 km3). Of all the lochs and lakes in Great Britain, it is the largest by surface area and the second largest (after Loch Ness) by water volume. Within the United Kingdom, it is surpassed only by Lough Neagh and Lough Erne in Northern Ireland and regarding the British Isles as a whole, there are also several larger loughs in the Republic of Ireland.
Traditionally a boundary between Stirlingshire and Dunbartonshire, Loch Lomond is currently split between the council areas of Stirling, Argyll and Bute and West Dunbartonshire. Its southern shores are about 14 miles (23 km) north of Glasgow, Scotland's largest city.
Loch Lomond is now part of Loch Lomond and the Trossachs National Park. Ben Lomond is on the eastern shore: 3,195 feet (974 m) in height and the most southerly of the Scottish Munro peaks. A 2005 poll of Radio Times readers voted Loch Lomond as the sixth greatest natural wonder in Britain.
The main arterial route along the loch is the A82 road which runs the length of its western shore. For a long time, this was a notorious bottleneck, with the route clogged with tourists during the summer months. It was upgraded in the 1980s and 1990s, although the stretch north of Tarbet remains unimproved.
The loch contains thirty or more other islands, depending on the water level. Several of them are large by the standards of British bodies of freshwater. Inchmurrin, for example, is the largest island in a body of freshwater in the British Isles. As in Loch Tay, several of the islands appear to be crannogs, artificial islands built in prehistoric periods.
English travel writer, H.V. Morton wrote:
What a large part of Loch Lomond's beauty is due to its islands, those beautiful green tangled islands, that lie like jewels upon its surface.
One of the loch's islands, Inchconnachan, is home to a colony of wallabies.
Loch Lomond Golf Club is situated on the south-western shore. It has hosted many international events including the Scottish Open. Another golf club, "The Carrick" has opened on the banks of the Loch adjacent to the Loch Lomond Club. The West Highland Way runs along the eastern bank of the loch. West Loch Lomond Cycle Path runs from Arrochar and Tarbet railway station, at the upper end of the loch, to Balloch railway station, at the south end. The 17-mile-long (28 km) long cycle path runs along the west bank.
At the south end of the loch near Balloch is a large visitor and shopping complex named Loch Lomond Shores. This was the venue for the Great Scottish Swim in 2013.
Loch Lomond is one of Scotland's premier boating and watersports venues and the scenery draws people from all over Scotland and beyond. The loch is open to every kind of watercraft including kayaks, canoes, windsurfers, jet skis, speedboats and cruisers and they are all very well represented. Loch Lomond Rescue Boat provides 24-hour safety cover on the loch. The Rescue Boat is a Volunteer Organisation and a Registered Charity. The National Park Authority also have other boats on the Loch such as The Brigadier. Police Scotland also operates on the Loch using RIBs and Jet Skis and work in conjunction with the National Park Authority.
The National Park Authority has tried to achieve a balance between land-based tourists and loch users, with environmentally sensitive areas subject to a strictly enforced 10 km/h (5.4 kn; 6.2 mph) speed limit, but the rest of the loch open to speeds of up to 90 km/h (49 kn; 56 mph).
Other leisure activities on the loch include cruises from the town of Balloch, operated by Sweeney's Cruises.
The Maid of the Loch was the last paddle steamer built in Britain. Built on the Clyde in 1953, she operated on Loch Lomond for 29 years. She is now being restored at Balloch pier by the Loch Lomond Steamship Company, a charitable organisation, supported by West Dunbartonshire Council.
Guided canoeing and canoe hire is available through some small companies such as SD Adventures
On 22 April 1940, a BOAC Lockheed Model 14 Super Electra (Loch Invar, registration G-AFKD) aircraft flying from Perth Airport to Heston Aerodrome in London crashed at Loch Lomond, killing all five passengers and crew.
The loch is featured in a well-known song which was first published around 1841. The chorus is:
Oh, ye'll tak the high road, and I'll tak the low road, And I'll be in Scotland afore ye; But me and my true love will never meet again On the bonnie, bonnie banks o' Loch Lomond.
The song has been recorded by many performers over the years, including jazz singer Maxine Sullivan, the Mudmen and Scottish-Canadian punk band the Real McKenzies. The original author is unknown. One story is that the song was written by a Scottish soldier who awaited death in enemy captivity; in his final letter home, he wrote this song, portraying his home and how much he would miss it. Another tale is that during the 1745 Rebellion a soldier on his way back to Scotland during the 1745–46 retreat from England wrote this song. The "low road" may be a reference to the Celtic belief that if someone died away from his homeland, then the fairies would provide a route of this name for his soul to return home. Within this theory, it is possible that the soldier awaiting death may have been writing either to a friend who was allowed to live and return home, or to a lover back in Scotland.