The West Siberian Plain, also known as Zapadno-sibirskaya Ravnina, 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 by the Altay 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 Omsk, Novosibirsk and Chelyabinsk.