The Volga is the principal waterway in Russia and is the longest river in Europe. It flows 2,300 mi (3,700 km) through western Russia. The river originates in the Valdai Hills northwest of Moscow and flows southeastward into the Caspian Sea, the world’s largest landlocked water body, near the city of Astrakhan. The Volga has about 200 tributaries, the most important of which are the Kama, the Oka, the Vetluga, and the Sura Rivers. Because of fluctuations in the level of the Caspian Sea, the delta has grown significantly in the past century and is one of the largest deltas in the world covering a total area of about 1.9 M ha.