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 distinct population of polar bears associated with the Barents Sea area. Almost all of the area of the Oblast belongs to the basin of the Arctic Ocean, with the major rivers being (west to east) Onega River, Northern Dvina River (with the major tributaries the Vychegda, the Vaga, and the Pinega), Kuloy River, Mezen River, and Pechora River (Shapkina River being a major tributary). A minor area in the west of the Oblast, most notably the basin of the Ileksa River, drains into the Lake Onega and eventually to the Baltic Sea. A very minor area in Kargopolsky District in