Plans for a new £140m hydro-electric power station in the Highlands able to generate enough energy for 37,000 homes have been given the go-ahead.
Work will begin on the scheme at Loch Ness next spring
Enterprise Minister Nicol Stephen said the Glendoe scheme, near Fort Augustus in Invernesshire, would yield economic and environmental benefits.
Scottish and Southern Energy (SSE) said construction would begin next spring, with the creation of 400 jobs.
It said it was the biggest scheme in Scotland for 40 years.
The scheme, on the western edge of the Monadhliath Mountains, will involve the construction of a 35-metre high, 1,000-metre dam at the head of Glen Tarff and the building of an underground power station inside Borlum Hill on the shore of Loch Ness.
It will involve collecting water from 75 sq km - either directly or via 8km of underground tunnels - in a new reservoir, about 600m above Loch Ness.
The power station will produce about 180 million units of green electricity in a year of average rainfall.
Operating at maximum capacity, SSE said the scheme would be able to generate enough electricity to power 250,000 homes and should be fully operational by 2008.
Mr Stephen said the "exciting project" would make a significant contribution to the Scottish Executive's target of generating 40% of Scottish electricity from renewable sources by 2020.
He added: "As well as the obvious environmental benefits, the Glendoe scheme has the potential to bring considerable economic opportunities to the area during the construction period.
An artist's impression of the new Glendoe scheme
"Today's approved Glendoe scheme is further evidence that even more of our electricity is generated from this clean source."
SSE chief executive Ian Marchant added: "The scheme confirms that there is much more to renewable energy than a dash of wind.
"As the most efficient hydro scheme in the country, it will be exceptionally flexible and will have a significant part to play in meeting peak demand for power."
Duncan McLaren, chief executive of Friends of the Earth Scotland, welcomed the announcement.
"If we are to fend off looming climate chaos, we urgently need to increase our renewable energy capacity," he said.
"We welcome schemes such as this which will help us to reduce our climate emissions.
"Hydro power schemes, in combination with power from wind and other sources, demonstrate that clean renewable energy can provide a mix of types of energy to meet our needs.
"This reaffirms our belief that Scotland can and should become a world leader in all forms of renewable energy."
Public bodies are being urged to make greater use of recycled materials in construction projects.
Environment Minister Ross Finnie has launched a consultation on setting targets for public procurement building contracts to include at least a 10% of recycled materials by March next year.