The White Sea is an important traffic centre of northwestern Russia. The White Sea – Baltic Canal links it through Onega Lake to the Baltic Sea and the major city and port of Saint Petersburg. The Baltic Sea, in turn, is connected by the Volga–Baltic Waterway to the Volga River, Black, Caspian, and Azov seas. The major ports on the White Sea are Arkhangelsk, Belomorsk, Onega, Mezen, Kem, Kandalaksha and Umba. Even though it is frozen in winter, boats can travel on the sea all year around because of the use of icebreakers.