Hydrology
Numberless lakes occupied the depressions, while a great many more had left evidences of their existence in the extensive marshes. Lake Onega covers 3,764 m², and reaches a depth of 400 ft (120 m). Lakes Zeg, Vygozero, Lacha, Loksha, Tulos, and Vodlozero cover from 140 to 480 m² each, and their crustacean fauna indicates a former connection with the Arctic Ocean. The south-eastern part of Lake Ladoga falls also within the government of Olonets. The rivers drain to the Baltic Sea and White Sea basins. To the former system belong Lakes Ladoga and Onega, which are connected by the Svir River and receive numerous streams; of these the Vytegra, which communicates with the Mariinsk canal-system, and the Oyat, an affluent of Lake Ladoga, are important for navigation.
Read more about this topic: Olonets Governorate