river in Leningrad oblast (province), northwestern Russia. The river issues from Lake Ladoga at Shlisselburg and flows 46 miles (74 km) west to the Gulf of Finland in the Baltic Sea. Its drainage basin covers 109,000 square miles (282,000 square km) and includes Lakes Ladoga, Onega, and Ilmen and the Svir and Volkhov rivers. Freeze-up lasts from early December to late April. The river derives importance not only from its navigability by large ships—it forms part of the White Sea–Baltic and Volga-Baltic waterways—but also from the presence of St. Petersburg city at its mouth.