Lake Baikal

A fifth of the planet’s unfrozen fresh water, in one lake

Lake Baikal fills a rift in southern Siberia, between Irkutsk Oblast and the Republic of Buryatia, where the Earth's crust is pulling apart by about 4 mm a year. It is 636 km long and 79 km wide, and at 1,642 metres it is the deepest lake in the world. Beneath its floor lie some 7 km of sediment, which puts the bottom of the rift 8 to 11 km below the surface, the deepest continental rift on Earth. It is also the oldest lake, at 25 to 30 million years, and the largest freshwater lake by volume, holding 22 to 23 per cent of the world's fresh surface water, more than all the North American Great Lakes combined. As many as 330 rivers feed it, and a single outlet, the Angara, drains it.

From early January to May or June the surface is ice, on average half a metre to 1.4 metres thick, and in winter the open water can be clear to 30 or 40 metres. Storms in summer and autumn raise waves as high as 4.5 metres.

Its age and isolation have produced what UNESCO calls one of the world's richest and most unusual freshwater faunas, and the lake is known as the Galapagos of Russia. The Baikal seal, the nerpa, lives nowhere else and feeds mostly on golomyankas, which with certain sculpins are the deepest-living freshwater fish in the world. Endemic sponges on the bottom can grow to a metre or more. The omul, an endemic whitefish, was for centuries the main local food, eaten salted or smoked. In 2017 Russia banned its commercial catch after its biomass more than halved in 15 years, and the Guardian reported thick mats of rotting Spirogyra algae on beaches near towns without proper sewage treatment.

The lake has carried many names. Chinese sources called it the North Sea; the Kurykans, in the sixth century, used a name meaning much water; the Buryats, who still herd on its eastern shore, called it Baygal nuur, the natural lake. In 1643 Kurbat Ivanov became the first European to see Baikal and Olkhon, its largest island, 72 km long. The railway around its southwestern end, part of the Trans-Siberian line built between 1896 and 1902, needed 200 bridges and 33 tunnels. UNESCO listed the lake in 1996.