Lake Onega is a lake in the north-west European part of Russia, located on the territory of Republic of Karelia, Leningrad Oblast and Vologda Oblast. It belongs to the basin of Baltic Sea, Atlantic Ocean, and is the second largest lake in Europe after Lake Ladoga. The lake is fed by about 50 rivers and is drained by the Svir River.
There are about 1650 islands on the lake. They include Kizhi, which hosts a historical complex of 89 orthodox wooden churches and other wooden constructions of 15th–20th centuries. The complex includes a UNESCO World Heritage site Kizhi Pogost. Eastern shores of the lake contain about 1200 petroglyphs (rock engravings) dated to 4th–2nd millennia BC. The major cities on the lake are Petrozavodsk, Kondopoga and Medvezhyegorsk.
The lake banks are low and are flooded with raising water level. They are therefore swampy and are rich in reed, hosting ducks, geese and swans. The coastal region is covered with dense virgin forests. Major tree types are coniferous, but also common are lime (linden), elm and European Alder. Common mammals include elk, brown bear, wolf, fox, hare, squirrel, lynx, pine marten, European badger, as well as American muskrat and mink which were introduced to the area in the early 20th century. About 200 bird species from 15 families have been observed in the lake basin.
Lake Onega features a large variety of fish and water invertebrates, including relicts of the glacial period such as lamprey. There are about 47 fish species from 13 families; they include sturgeon, landlocked salmon, brown trout, European smelt, grayling, roaches, Crucian carp, whitefishes, char, pike, European cisco, common dace, silver bream and carp bream.