The Onega (Russian: Оне́га; Finnish: Äänisjoki) is a river in Kargopolsky, Plesetsky, and Onezhsky Districts of Arkhangelsk Oblast in Russia.

The whole valley of the Onega is populated, with the exception of the stretch between Severoonezhsk and Yarnema, in Plesetsky District.

155 kilometres (96 mi) of the river's lower course, between the village of Gorodok and the selo of Porog, is listed in the State Water Register of Russia as navigable.

Some of the finest monuments of the northern wooden architecture are located in the basin of the Onega, including ensembles of Lyadiny, Saunino Pogost, Krasnaya Lyaga, and Bolzhaya Shalga.

[1] The Onega flows among the coniferous forests (taiga of spruce, pine, and larch), mostly among the swamps.