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
Battle of Bolshie Ozerki of the intervention to involve American forces, though they successfully defended their camp from a Russian attack at Romanovka composed of forces that greatly outnumbered them two months later and inflicted hundreds of casualties during the Suchan Valley Campaign the following month. Allied forces began to withdraw rapidly from northern Russia shortly thereafter. Bolshie Ozerki was a small village situated between the port city of Onega and an important Allied position at Obozerskaya Station, along the Arkhangelsk-Vologda railroad. Because the port of the main Allied base at Arkhangelsk froze every winter, reinforcements had to be brought overland to the front