Russia has diverse physical geography and climate. The Russian Plain covers much of European Russia and Western Siberia, containing tundra, marshes, and taiga forest. Major rivers include the Volga, Ob, Yenisei, and Lena, which flow north through the plain. Lake Baikal in southern Siberia is the largest freshwater lake by volume in the world. Russia's climate varies from polar in the Arctic to subarctic and humid continental farther south.