Southern Vietnam is dominated by the rich agricultural lands of the Mekong Delta, the nation??? major source of rice, fruit and vegetable production. The land is alluvial and low-lying, with marshlands and mangrove forests to the west and south. During the rainy season, water covers a third of the delta, with flooding up to 13 ft (4 m). In places, salt water encroaches into the delta for up to 30 m (48 km). Although extraordinarily fertile, parts of the Delta have yet to come under cultivation.