Lake Cadagno (26 hectares / 64 acres) is situated at 1923 m above sea level on the South face of the Gotthard massif. Its waters show a permanent stratification due to the meromixis phenomenon. The lower layer (monimolimnion) is rich in dissolved salts brought by sulphureous sublacustrine springs, and is separated from the upper oxygenated layer (mixolimnion) by a transition zone (chemocline) with a large population of phototrophic bacteria formed mainly by the species Chromatium okenii. This anaerobic bacterial photosynthesis constitutes an additional primary production that, added to the normal production of phytoplancton, determines a high trophic capacity, which is unusual in a small alpine lake. During the winter, this lake is used for hydroelecric purposes and its level is brought down about 3 meters.