Lake Baikal (Russian: о́зеро Байка́л, tr. Ozero Baykal; IPA: [ˈozʲɪrə bɐjˈkal]; Buryat: Байгал нуур, Mongolian: Байгал нуур, Baygal nuur, meaning "nature lake";) is a rift lake in the south of the Russian region of Siberia, between the Irkutsk Oblast to the northwest and the Buryat Republic to the southeast.
Lake Baikal is the most voluminous freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water, and at 1,642 m (5,387 ft), the deepest. It is also among the clearest of all lakes, and thought to be the world's oldest lake at 25 million years.
Similar to Lake Tanganyika, Lake Baikal was formed as an ancient rift valley, having the typical long crescent shape with a surface area of 31,722 km2 (12,248 sq mi). Baikal is home to more than 1,700 species of plants and animals, two thirds of which can be found nowhere else in the world and was declared a UNESCO World Heritage Site in 1996. It is also home to Buryat tribes who reside on the eastern side of Lake Baikal, rearing goats, camels, cattle and sheep, where the regional average temperatures vary from a minimum of −19 °C (−2 °F) in winter to maximum of 14 °C (57 °F) in summer. Lake Baikal is nicknamed "Older sister of Sister Lakes (Lake Khövsgöl and Lake Baikal).