Lake Baikal is a rift lake located in Russia situated in southern Siberia between the federal subjects of Irkutsk Oblast to the northwest and Buryatia to the southeast.
With 23,615.39 km3 (5,670 cu mi) of water, Lake Baikal is the world's largest freshwater lake by volume, containing 22–23% of the world's fresh surface water, more than all of the North American Great Lakes combined. It is the world's deepest lake, with a maximum depth of 1,642 m (5,387 ft), and the world's oldest lake, at 25–30 million years. At 31,722 km2 (12,248 sq mi)—slightly larger than Belgium—it is the world's seventh-largest lake by surface area. It is among the world's clearest lakes.
Baikal is home to thousands of species of plants and animals, many of them endemic to the region. It is also home to Buryat tribes, who raise goats, camels, cattle, sheep, and horses on the eastern side of the lake, where the mean temperature varies from a winter minimum of −19 °C (−2 °F) to a summer maximum of 14 °C (57 °F).
The region to the east of Lake Baikal is referred to as Transbaikalia or as the Transbaikal, and the loosely defined region around the lake itself is sometimes known as Baikalia. UNESCO declared Baikal a World Heritage Site in 1996.
Lake Baikal is rich in biodiversity. It hosts more than 1,000 species of plants and 2,500 species of animals based on current knowledge, but the actual figures for both groups are believed to be significantly higher. More than 80% of the animals are endemic.
The watershed of Lake Baikal has numerous floral species represented. The marsh thistle (Cirsium palustre) is found here at the eastern limit of its geographic range.
Submerged macrophytic vascular plants are mostly absent, except in some shallow bays along the shores of Lake Baikal. More than 85 species of submerged macrophytes have been recorded, including genera such as Ceratophyllum, Myriophyllum, Potamogeton, and Sparganium. The invasive species Elodea canadensis was introduced to the lake in the 1950s. Instead of vascular plants, aquatic flora is often dominated by several green algae species, notably Draparnaldioides, Tetraspora, and Ulothrix in water shallower than 20 m (65 ft); although Aegagrophila, Cladophora, and Draparnaldioides may occur deeper than 30 m (100 ft). Except for Ulothrix, there are endemic Baikal species in all these green algae genera. More than 400 diatom species, both benthic and planktonic, are found in the lake, and about half of these are endemic to Baikal; however, significant taxonomic uncertainties remain for this group.