Lac Pavin

Lac Pavin or Lake Pavin is a meromictic crater lake, located in the Dore mountains, in Auvergne, in the territory of the commune of Besse-et-Saint-Anastaise, Puy-de-Dôme department of France, between Besse-en-Chandesse and Super-Besse. Formed by phreatomagmatism 6,900 years ago, this crater lake is the youngest volcano in mainland France

It gives its name to a cheese: Pavin cheese.

Source: Wikipedia