Draining most of western Russian, the Volga is the largest river in Europe. From its source in the Valdai Hills north east of Moscow the river flows east and south east to the Caspian Sea. A large number of tributaries make up the Volga river system the delta where the river enters the Caspian is composed of hundreds of channels and lies 28 m below sea level. For three months of the year the river is frozen for most of its length, the presence of a large number of dams has improved navigation but has reduced the river’s flow. Consequently the river is suffering from pollution compounded by the fact that it flows through some of the most populated area of the country and includes an important agricultural area. Half of all river freight in Russia uses the Volga which is connected to the Black sea via the Don river and canals. The Volga is the national river of Russia and it and its drainage basin are located entirely within the Russian Federation.