The engineer Edward MacColl was asked to look at the possibility of using it for a hydro-electric sceme in 1936, while working for the Central Electricity Board.

[6] With both MacColl and Williamson having a good knowledge of the potential of Loch Sloy, this became the Board's first constructional scheme.

There were no issues with fishing rights, because of the nature of Inveruglas Water, and nearby Clydeside provided a ready market for the power generated.

When laid before Parliament, two smaller projects were included, at Kyle of Lochalsh and Loch Morar, which demonstrated the Board's commitment to supplying remote areas where it would normally be uneconomic to do so.

[7] The Board had hoped that the passage of the scheme through Parliament would be reasonably smooth, but most of the objections that had been used to stop hydro-electric development in the 1930s were raised again.

The Secretary of State decided that a public enquiry was necessary, and this was held in Edinburgh at the end of 1944, with John Cameron KC acting as chairman.

It took six days,[8] and the Board's case was not helped by the fact that they had moved the site for the power station after publishing the original plans, and had failed to secure agreement from the Ministry of War Transport over the need to reroute the Loch Lomond trunk road around the site of the power station.

[9] However, Cameron eventually decided that their plans for future development in the area were too optimistic and speculative to be realistic, and that the Board's contention that the scheme was in the public interest was correct.

Obtaining Portland cement also proved difficult, as no local suppliers could handle the quantities needed.

The contract was completed late, due to a chronic shortage of steel and very wet weather, but by 1950 Arrol had joined the power station to the valve house, some 1,500 feet (460 m) away.

Following Matthew Ochterlony's death in 1946, the scheme was progressed by Tarbolton, but he died in July 1947, and his architectural practice managed the construction subsequently.

[20] The building was constructed by Hugh Leggat, who were faced with incessant rain during 1947 and 1948, and a mass exodus of workers in 1947, who were not happy with working conditions or the quality of the food in the camps.

Nuttall had completed the main tunnel by early 1949, and teams of men spread out over the uplands to construct these structures.

Unlike the high-profile dam, main tunnel and power station, this attracted little attention in the press,[22] although one event did.

A pipeline runs to another dam on Allt Sugach, which again flows into Loch Long via Loin Water.

[24][25] The rest of the system captures water that would otherwise flow into Loch Lomond, either directly or via the River Falloch.

The tunnel heads northwards to Srath Dubh-Uisge, where six dams and an aqueduct are shown on the southern slopes of the valley, connecting to six tributaries.

[24][25] While all this was going on, another team of men were erecting pylons to carry the 132 kV lines from the switching station at Inveruglas to Windyhill, on the outskirts of Glasgow.

[26] On 18 February 1950, Sir Edward MacColl, who had only recently been knighted, switched on the first generator set at Sloy at 3:15 pm.

[27] Residents of Tarbet, further south on Loch Lomond, and at Arrochar on Loch Long, had been supplied with electricity from the temporary diesel generating station since April 1948, when Miss Mary MacFarlane, the oldest resident of the village, aged 96, had switched on the new supply.

[30] The facility is operated by Scottish and Southern Energy, and is normally in standby mode, ready to generate electricity to meet sudden peaks in demand.