Lake Baikal, Russian Ozero Baykal, also spelled Ozero Bajkal, lake located in the southern part of eastern Siberia within the republic of Buryatia and Irkutsk oblast (province) of Russia. It is the oldest existing freshwater lake on Earth (20 million–25 million years old), as well as the deepest continental body of water, having a maximum depth of 5,315 feet (1,620 metres). Its area is some 12,200 square miles (31,500 square km), with a length of 395 miles (636 km) and an average width of 30 miles (48 km). It is also the world’s largest freshwater lake by volume, containing about one-fifth of the fresh water on Earth’s surface, some 5,500 cubic miles (23,000 cubic km). Into Lake Baikal flow more than 330 rivers and streams, the largest of which include the Selenga, Barguzin, Upper (Verkhnyaya) Angara, Chikoy, and Uda.