a river in Arkhangel’sk Oblast of the RSFSR. It is 416 km long and drains an area of 56,900 sq km. After issuing from Lake Lacha, it flows through a rolling plain. Broad stretches of up to 450 m alternate with narrow sections (40 m) with rapids. About 75 km from its mouth the river divides into the Bol’shaia Onega and the 20-km Malaia Onega. Entering into the Onega Bay of the White Sea, the Onega forms a delta, whose main channels are the Dvinskii and the Karel’skii.
The Onega is fed chiefly by snow, and in its upper reaches the flow is regulated by lakes. High water lasts from May to June, with the lowest water level in March. The fluctuation in water level is 3.4 m at the source, 9.7 m in the middle course, and 6 m in the lower reaches. At the river’s mouth there are tides of up to 1.5 m. The river discharges at an average rate of 74.1 cu m per sec at its source and 505 cu m per sec at its mouth; its maximum discharge is 4,530 cu m per sec, and its minimum discharge, 82.6 cu m per sec. The Onega freezes between late October and early December (the areas with rapids freeze in January and February), and it breaks up in mid-April or May. Salmon and navaga are caught at the mouth of the river, which is also used for floating timber. Stretches of the river are navigable. The principal cities along the river are Onega, at the mouth, and Kargopol’.