ONEGA, the largest lake in Europe next to Ladoga, having an area of 3764 sq. m. It is situated in the government of Olonets in European Russia, and, discharging its waters by the Svir into Lake Ladoga, belongs to the system of the Neva. The lake basin extends north-west and south-east, the direction characteristic of the lakes of Finland and the line of glacier-scoring observed in that region. Between the northern and southern divisions of the lake there is a considerable difference: while the latter has a comparatively regular outline, and contains hardly any islands, the former splits up into a number of inlets, the largest being Povyenets Bay, and is crowded with islands (e.g. Klimetsk) and submerged rocks. It is thus the northern division which brings the coast-line up to 870 m. and causes the navigation of the lake to be so dangerous. The north-western shore between Petrozavodsk and the mouth of the river Lumbosha consists of dark clay slates, generally arranged in horizontal strata and broken by protruding, parallel ridges of diorite, which extend far into the lake. The eastern shore, as far as the mouth of the Andoma, is for the most part alluvial, with outcroppings of red granite and in one place (the mouth of the Pyalma) diorite and dolomite. To the south-east are sedimentary Devonian rocks, and the general level of the coast is broken by Mount Andoma and Cape Petropavlovskiy (160 ft. above the lake); to the south-west a quartz sandstone (used as a building and monumental stone in St Petersburg) forms a fairly bold rim. Lake Onega lies 125 ft. above the sea. The greatest depths, 318 to 408 ft., occur at the entrance to the double bay of Lizhemsk and Unitsk. On the continuation of this line the depth exceeds 240 ft. in several places. In the middle of the lake the depth is 120 to 282 ft., and less than 120 ft. in the south. The lake is 145 m. long, with an average breadth of 50 m. The most important affluents, the Vodka, the Andoma and the Vytegra, come from the east. The Kumsa, a northern tributary, is sometimes represented as if it connected the lake with Lake Seg, but at the present time the latter drains to the White Sea. The Onega canal (45 mi. long) was constructed in 1818–1851 alongthe southern shore in order to connect the Svir (and hence Lake Ladoga and the Baltic) with the Vytegra, which connects with the Volga. Lake Onega remains free from ice for 209 days in the year (middle of May to second week of December). The water is at its lowest level in the beginning of March; by June it has risen 2 ft. A considerable population is scattered along the shores of the lake, mainly occupied in the timber trade, fisheries and mining industries. Salmon, palya (a kind of trout), burbot, pike, perch pike and perch are among the fish caught in the lake. Steamboats were introduced in 1832.
The river Onega, which, after a course of 250 m., reaches the Gulf of Onega, an inlet of the White Sea. has no connexion with Lake Onega. At the mouth of this river (on the right bank) stands the town and port of Onega (pop. 2604 in 1897), which dates from settlements made by the people of Novgorod in the 15th century, and known in history as Ustenskaya or Ustyanskaya. It has a cathedral, erected in 1796. (P. A. K.; J. T. Be)