The only meromictic lake in France, Lake Pavin has high methane concentrations in its deep water layer. Methane is one of the main greenhouse gases. It is mainly produced and consumed by the metabolic activity of microorganisms of the Archaea and Bacteria types. The environmental conditions of the freshwater lake of Pavin's ecosystem indeed promote methanogenesis to the detriment of other terminal processes of degradation of organic matter. Emissions of methane to the atmosphere, therefore, remain low around Lake Pavin.