Russia's second largest city and its former capital, St. Petersburg is a major seaport, rail junction, and industrial, cultural, and scientific center. Although the harbor is frozen for three or four months annually, icebreakers have prolonged the navigation season. The seaport is one of the world's largest, but it handles relatively little traffic because the volume of foreign trade for Russia is small. The river port, one of the most important in the country, stands at the end of two artificial waterways, the Volga-Baltic and the White Sea–Baltic. A series of canals within the city carries considerable cargo. Neva Bay is separated from the Gulf of Finland at Kotlin Island by a 15.8-mi (25.4-km) flood-control dam (completed 2011) that allows for closing the navigation channels to prevent the flooding of the city; the causeways, bridges, and a tunnel built in conjunction with the dam form part of the city's ring road. St. Petersburg's diverse industries include shipbuilding, metallurgy, oil refining, printing, woodworking, food and tobacco processing, and the manufacture of machinery, electrical equipment, chemicals, pharmaceuticals, automobiles, and textiles.