PLANET EARTH Freshwater

Early explorers told tales of lakes that smoked, as if on fire. But these spiraling columns hundreds if meters high are mating flies. Once the flies have mated, they will all drop to the water surface, release their eggs and die. Malawi may look like an inland sea, but it's dwarfed by the world's largest lake - Baikal in Eastern Siberia.



400 miles long and over a mile deep, Baikal contains one fifth of all the fresh water found in our planet's lakes and rivers. For five months of the year it's sealed by an ice sheet over a meter thick. Baikal is the oldest lake in the world and, despite the harsh conditions, life flourishes here in isolation. 80 percent of its species are found nowhere else on Earth, including the world's only fresh water seal.



With this seal and its marine-like（类似海洋的） forests of sponges Baikal seems more like an ocean than a lake. There are shrimp-like crustaceans（甲壳类动物） - giant amphipods（两足动物） - as large as mice. They are the key scavengers（食腐动物） in this lake. The water here is just too cold for the bacteria that normally decompose the dead.