The government agency claims that the scale of the development would be out of place in an area renowned for its dramatic scenery. The scheme would include a luxury hotel, leisure and retail facilities, two 18-hole golf courses, a restaurant and more than 100 houses.
SNH is concerned by its proximity to special areas of conservation, including the fourth largest Caledonian pine wood in Scotland.
An application is under consideration at Perth and Kinross Council. RSPB Scotland and land conservation charity the John Muir Trust have already lodged objections to the development.