The Lochaber Hydroelectric Scheme, built between 1924 and 1943 by the British Aluminium Company, supplies power to the Fort William aluminium smelter using water from the River Spean and River Spey catchments. Centred on Loch Treig and Laggan Reservoir, the system includes 29 km of tunnels carved through the mountains and remains one of the UK’s most ambitious early hydro projects. Ownership has passed from Alcan to Rio Tinto, and now to GFG Alliance, which continues to operate both the hydro scheme and smelter.

The scheme’s vast catchment—over 780 km²—feeds water through a 15-mile pressure tunnel around Ben Nevis to a powerhouse near Fort William. Initially using twelve Pelton turbines, the plant powered aluminium production by 1929, later expanding during World War II to meet rising demand. Major civil works included the Laggan and Treig Dams, linked by tunnels and aqueducts, and the Spey Dam diversion built by Balfour Beatty and Canadian engineers in the 1940s.

In 2008, a €30 million upgrade replaced the original turbines with five 17 MW Francis units, boosting capacity by 20%. The scheme continues to deliver renewable energy while standing as a landmark of Scottish engineering — a fusion of early 20th-century ambition and enduring hydroelectric innovation.