Loch Sloy, which sits in the hills several hundred feet above Loch Lomond, was the subject of the first scheme undertaken by the North of Scotland Hydro Electricity Board in 1945. Sloy was to provide the water for a generating station built by the shores of Loch Lomond. The work was difficult and slow; some of the labour was provided by German prisoners of war. By the time the project was complete, Loch Sloy had increased in depth by 155 feet, doubled in length, and collected rainfall from a catchment four times larger than it had before. A tunnel was driven through Ben Vorlich, which sits between Loch Sloy and Loch Lomond, to take the water to the top of the slope above the power station itself.