More than 600 water voles have been released in the Trossachs.
The rare, semi-aquatic animals, once a common sight across the UK, have become extinct in the area over the last 25 years.
The three-year project, the first of its kind in Scotland, involves about 1,000 water voles being released on restored wetlands in Aberfoyle.
The animals' decline is blamed on a loss of habitat and the introduction of the more aggressive American mink.
The vole was immortalised in the fictional character of Ratty, the water rat in Kenneth Grahame's book The Wind in the Willows, published a century ago.
Environment Minister Roseanna Cunningham described the animal as an important cultural and ecological component of Scotland's countryside.
"This sets a new precedent for conservation projects in the Trossachs and across Scotland," she added.
All of the animals being released have been bred from voles originally captured on a development site near Glasgow.
The project is being focused along a 20km stretch of mainline watercourse in the Duchray and Kelty areas, both of which flow through Loch Ard Forest.
Katy Freeman from the Forestry Commission, who is helping to co-ordinate the project, said: "The restored wetlands will help to establish a new population of water voles, which in turn will enrich and enhance the habitat for a wide range of other species.
"It's great for biodiversity and the water voles will be a great draw for visitors to the area.
"The project is also a great way of educating people about the importance of maintaining the rich network of wildlife and habitats in the area."
The scheme is being led by Forestry Commission Scotland, and is being partnered by SNH, the Royal Zoological Society of Scotland and the Kilgarth Development Company and Loch Lomond & The Trossachs National Park Authority.