Half the water flowing into the lake comes down the Selenga River in the southeast.

The rest comes from more than 330 other rivers and streams, many of them flowing from the surrounding mountains. Lake Baikal’s only outlet is the Angara River, which flows westward from the lake’s southwestern end.

Lake Baikal has about 45 islands and islets, of which the two biggest are Olkhon, about 270 square miles (700 square kilometers) in area, and Great Ushkany, which covers only about 3.6 square miles (9.4 square kilometers).

Olkhon is a region of forests and grasslands that supports deer, brown bears, and a wide range of birds.

Great Ushkany is rocky, the site of the largest rookery of Baikal seals. Many of the other islands are little more than rocks, used as roosts by water birds.