Loch Treig is a 9 km freshwater loch

Loch

Loch is the Irish and Scottish Gaelic word for a lake or a sea inlet. It has been anglicised as lough, although this is pronounced the same way as loch. Some lochs could also be called a firth, fjord, estuary, strait or bay...

 situated in a steep-sided glen

Glen

A glen is a valley, typically one that is long, deep, and often glacially U-shaped; or one with a watercourse running through such a valley. Whittow defines it as a "Scottish term for a deep valley in the Highlands" that is "narrower than a strath."...

 20 km east of Fort William

Fort William, Scotland

Fort William is the second largest settlement in the highlands of Scotland and the largest town: only the city of Inverness is larger.Fort William is a major tourist centre with Glen Coe just to the south, Aonach Mòr to the north and Glenfinnan to the west, on the Road to the Isles...

, in Lochaber

Lochaber

District of Lochaber 1975 to 1996Highland council area shown as one of the council areas of ScotlandLochaber is one of the 16 ward management areas of the Highland Council of Scotland and one of eight former local government districts of the two-tier Highland region...

, Highland

Highland (council area)

Highland is a council area in the Scottish Highlands and is the largest local government area in both Scotland and the United Kingdom as a whole. It shares borders with the council areas of Moray, Aberdeenshire, Perth and Kinross, and Argyll and Bute. Their councils, and those of Angus and...

, Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

. While there are no roads alongside the loch, the West Highland Line

West Highland Line

The West Highland Line is considered the most scenic railway line in Britain, linking the ports of Mallaig and Oban on the west coast of Scotland to Glasgow. The line was voted the top rail journey in the world by readers of independent travel magazine Wanderlust in 2009, ahead of the iconic...

 follows its eastern bank.

Since 1929 Loch Treig has been a reservoir, retained behind the Treig Dam, forming part of the Lochaber hydro-electric scheme, which required diversion of the West Highland Railway

West Highland Railway

The West Highland Railway was one of the last main lines to be built in Scotland. It is one of the most scenic railway lines in Britain, linking Fort William on the west coast to Glasgow. It was originally operated by the North British Railway.- History :...

. The increase in water level following the construction of the dam submerged the small communities of Kinlochtreig and Creaguaineach at the lochs southern end, which had historically hosted locally important markets and had been the end point of cattle drove roads.