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
Onezhsky District Porog; there is regular passenger navigation. There is also limited passenger service on the Onega Bay. Onega is served by the Onega Airport which has weekly passenger flights to Arkhangelsk and to the "selo" of Purnema on the Onega Peninsula. Onezhsky District has a very high concentration of historical, archaeological, and architectural monuments. The district contains thirty-two objects classified as cultural and historical heritage by Russian Federal law, and additionally eighteen objects classified as cultural and historical heritage of local importance. Most of these are wooden churches and chapels. The monuments classified as historical and architectural heritage are the following: