Leningrad Oblast of two great lakes of the European Part of Russia, Lake Ladoga and Lake Onega. Its northeastern part, between the Gulf of Finland and Lake Ladoga, occupies the Karelian Isthmus. Some islands in the Gulf of Finland (including Kotlin, on which the city of Kronstadt has been built) and Lake Ladoga (including Konevets) also belong to the oblast. Much of the area of the oblast belongs to the drainage basin of the Neva, which is the only outflow of Lake Ladoga. Whereas the Neva, which flows to the Gulf of Finland (the city of Saint Petersburg is located in its
Lake Ladoga Neva to the Svir. The basin of Lake Ladoga includes about 50,000 lakes and 3,500 rivers longer than 10 km. About 85% of the water inflow is due to tributaries, 13% is due to precipitation, and 2% is due to underground waters. Geologically, the Lake Ladoga depression is a graben and syncline structure of Proterozoic age (Precambrian). This "Ladoga–Pasha structure", as it known, hosts Jotnian sediments. During the Pleistocene glaciations the depression was partially stripped of its sedimentary rock fill by glacial overdeepening. During the Last Glacial Maximum, about 17,000 years BP, the lake served likely as a channel that