Lake Baikal 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)".
Lake Baikal was known as the "North Sea" (北海 Běihǎi) in historical Chinese texts. It was situated in the then Xiongnu territory that stretched from the empire of the Han Dynasty in the south, to the Siberian taiga north of the lake, and saw military excursions led by the army of the Han Dynasty engaging the Xiongnu during the Han-Hun Wars.Little was known to Europeans about the lake until Russia expanded into the area in the 17th century. The first Russian explorer to reach Lake Baikal was Kurbat Ivanov in 1643.