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 non-freezing harbour of Murmansk, lost its significance as the main trading harbour of the Russian Empire. However, in the early 20th century Arkhangelsk was an important starting point for Russian Arctic expeditions. For instance, in the 1830s Pyotr Pakhtusov sailed twice from Arkhangelsk to investigate and map Novaya Zemlya. In 1932 the "Icebreaker Sibiryakov" under the command of Vladimir Voronin, sailing from Arkhangelsk, crossed the Northern Sea Route in a single navigation. In 1918 and 1919, Arkhangelsk Governorate became one of the most active battlegrounds of the Civil War in Russia. On August 2, 1918, Arkhangelsk was occupied