Ural River, a river in southwestern Russia. It is sometimes considered part of the boundary between Europe and Asia. From its source in the southern Ural Mountains of Russia, the river flows south through Kazakhstan past the city of Orsk, then west to Uralsk, and then south again. The Ural empties into the Caspian Sea at Guryev. The river's total length is 1,575 miles (2,535 km). Much of the extreme northwestern part of Kazakhstan is irrigated by waters from the Ural.