Lake Mogilnoye (Kildin)

On Kildin island in the Barents Sea, separated from the mainland by the Kildin Strait, lies Lake Mogilnoye — a relict meromictic basin, the only one in Russia (analogues are known in Canada, Iceland, Greenland and Palau). The lake is small — 560 by 280 metres, up to 17 metres deep — but its water is stratified into four layers of different salinity: from nearly fresh at the top to over 30 per mille at the bottom. The layers do not mix: above is a freshwater zone of up to 5 metres; deeper — marine fauna (sea anemones, jellyfish, starfish) at a salinity of about 22 per mille; at the bottom — the realm of purple bacteria producing hydrogen sulphide. The cause is sea water seeping through a 70-metre-wide barrier separating the lake from the Barents Sea. The lake's estimated age is about a thousand years. The lake is home to the endemic Kildin cod, listed in the Red Book. Since 1985 Mogilnoye has been a hydrological nature monument of republican significance.