Lake Annecy is a perialpine lake in Haute-Savoie in France.
It is the third largest lake in France, after the Lac du Bourget and Lac de Grand-Lieu, if the French part of Lake Geneva (which is also partly in Switzerland) is excluded. It is known as "Europe's cleanest lake" because of strict environmental regulations introduced in the 1960s. It is a popular tourist destination known for its swimming and water sports.
The lake was formed about 18,000 years ago, at the time the large alpine glaciers melted. It is fed by many small rivers from the surrounding mountains (Ire, Eau morte, Laudon, Bornette and Biolon), and from a powerful underwater source, the Boubioz, which enters at 82 m depth.