Lake Onega is relatively cold, with temperatures below for half of the year and average summer temperatures of about . The catchment area of drains into the lake via 58 rivers and more than 110 tributaries, including the Shuya, Suna, Vodla, Vytegra and Andoma. The only outgoing River Svir, which marks the southern boundary of Karelia, runs from the southwestern shore of Lake Onega to Lake Ladoga and continues as the Neva River to the Gulf of Finland. The White Sea–Baltic Canal runs through the lake from the White Sea to the Baltic Sea. The Volga–Baltic Waterway connects Onega Lake with the
Arkhangelsk Governorate Arkhangelsk Oblast (and later the Arkhangelsk Viceroyalty) was subdivided into seven uyezds (the administrative centers, which all had the town status, are given in parentheses), Mezen, Onega, and Pinega were incorporated as towns in 1780 just to become the uyezd towns. Kola was incorporated in 1784. In 1801, portions of the Povenetsky Uyezd were transferred to the Olonets Governorate, while the Kemsky Uyezd, with its center in Kem, was left to remain in the Arkhangelsk Governorate. In 1854, the town of Kola was destroyed during the Crimean War, and Kolsky Uyezd was merged into the Kemsky Uyezd. In 1883, the