The West Siberian Plain is a large plain that occupies the western portion of Siberia, between the Ural Mountains in the west and the Yenisei River in the east, and the Altai Mountains on the southeast. Much of the plain is poorly drained and consists of some of the world's largest swamps and floodplains. Important cities include Chelyabinsk, Novosibirsk, Omsk, and Tomsk, as well as Surgut and Nizhnevartovsk. Winters on the West Siberian Plain are harsh and long.