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 also navigable in the lower course. The Onega is not navigable except for the two relatively short stretches because of the rapids. However, except for the lower course of the Vychegda and some parts of the Northern Dvina, there is currently very little or no regular passenger navigation on these rivers. They are used for cargo traffic though. In 1765, a road was built between Saint-Petersburg and Arkhangelsk, mainly for postal service. The road still exists and passes Kargopol and Plesetsk, and it has been paved in 2011. One of the principal highways in Russia, M8, connects Moscow and Arkhangelsk,