Lake Cadagno, 1923 meters above sea level, is a rare example of crenogenic meromixis. Its waters show a permanent stratification due to a natural geological phenomenon. The lower abounds with dissolved mineral salts (sulphate, magnesium, calcium, carbonate) originating from sublacustrine springs, whereas the separate upper layer is permanently oxygenated. Anaerobic phototrophic bacteria belonging to the species Chromatium okenii thrive between the two layers where they find ideal conditions for their development. Such an ecosystem provides a good opportunity to study the metabolisms connected with eutrophication on a stable model, as it is well-known that one of the advanced stages of eutrophication is biogenic meromixis.