Dniester River, a large river in eastern Europe. From its source in the Carpathian Mountains in the Ukrainian district of Galicia it flows southeastward for 865 miles (1,390 km) through Ukraine and Moldova to the Black Sea. Its course is winding, and it reaches the Black Sea through an estuary near Odessa. The Dniester has been made navigable except in its far upper course. The Dniester formed the Romanian-Soviet border from 1918 until 1940, when Russia recovered Bessarabia.