Volga (Slav 'river'), the greatest river in Russia and the longest in Europe, having a course of over 900 miles as the crow flies, or, following its principal sinuosities, of 2400 from its source among the Valdai Hills in Novgorod to its seventy mouths in the Caspian. Over a mile broad about the middle of its course, it is navigable from near its source, and a system of canals and its numerous tributaries make it one of the most important waterways in the world, communicating with the White Sea, Euxine, Baltic, and Gulf of Finland, as well as with the Don, Dniester, Dnieper, Dwina, and other rivers. Some 15,000 vessels, including 500 steamers, navigate the Volga. Traffic ceases in winter, when the waters are frozen. The fisheries (sturgeon, carp, and pike) are of great importance. The navigation is impeded by shoals and banks. The principal tributaries are the Oka, Kama, Mologa, and Viatka. The chief towns on the Volga are Jaroslav, Kostroma, Nijni Novgorod, Kazan, Simbirsk, Stavropol, and Samara.