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 Oblast and the selo of Leshukonskoye, and there are still no roads into the Nenets Autonomous Okrug, on the left bank of the Onega downstream from Severoonezhsk, and very few roads on the right bank of the Northern Dvina. Many rivers can only be crossed by ferry boats, which means they cannot be crossed during the ice melting period. There is regular bus service on the main roads. The principal railway line in the oblast is the railroad connecting Moscow and Arkhangelsk. The piece between Vologda and Arkhangelsk was constructed in 1890s and passed through previously uninhabited areas between the valleys