Lake Ladoga (lä´dōgə, Rus. lä´dəgə), Finnish Laatokka, Rus. Ladozhskoye Ozero, c.7,000 sq mi (18,100 sq km), NW European Russia, in Karelia, NE of St. Petersburg. The largest lake in Europe, it is c.130 mi (210 km) long and c.80 mi (130 km) wide and has a maximum depth of 738 ft (225 m). Located on the heavily glaciated Baltic Shield, the lake has shores that are low and marshy in the south, rocky and indented in the north. It is subject to autumn storms and freezes every year for two months in the north and four months in the south. Chief among the many rivers that feed the lake are the Svir, descending from Lake Onega; the Vuoska, which forms the outlet of the Saimaa lake system of Finland; and the Volkhov, coming from Lake Ilmen. The main outlet is the Neva, which flows W into the Gulf of Finland at St. Petersburg. The fortress at Petrokrepost commands the Neva's exit from the lake. Among the many islands in the northern part of the lake is Valaam (Finnish Valama or Valamo), with a famous Russian monastery dating from the 12th cent. or earlier. Until the Finnish-Russian War of 1939–40, the northern part of the lake belonged to Finland; cession of the Finnish shore to the USSR was confirmed by the peace treaty of 1947. During the defense of St. Petersburg (then Leningrad) against the Germans in World War II, the frozen Lake Ladoga was the lifeline by which Leningrad was supplied in the winters from 1941 to 1943. Because of the difficulties of navigation, the southern shore of Lake Ladoga is paralleled by the Ladoga Canals, c.100 mi (160 km) long, connecting the Svir and Neva rivers and forming part of the Mariinsk System (see Volga-Baltic Waterway) and the Baltic–White Sea Canal System.