The four Russian rivers mentioned in the crossword solutions are the Lena, Ural, Volga, and Neva. The Lena is the longest river in Siberia, flowing 4, 400 miles from its source in the Baikal Mountains to the Laptev Sea. The Ural River is a major river in western Russia, flowing 1, 509 miles from its source in the Ural Mountains to the Caspian Sea. The Volga is the longest river in Europe, stretching 2, 294 miles from its source in the Valdai Hills to the Caspian Sea. Finally, the Neva is a river in northwestern Russia, flowing 74 miles from Lake Ladoga to the Gulf of Finland.