Lake Onega water per year, of which 46% are industrial and household water, 25% is stormwater runoff and 16% is melioration-related drainage. This drainage contains of phosphorus and of nitrogen; respectively of these elements are removed through the River Svir whereas the rest accumulates in the lake. Ships and motor boats (about 8,000 units) bring oil pollution at the level of about per navigation year, as well as phenols (), lead () and oxides of sulfur, nitrogen, and carbon. The lake basin is a major source of granite, marble and black schist in Russia which have been exploited in the area since
Lake Onega Volga River, Caspian Sea and Black Sea. The Onega Canal, which follows the southern banks of the lake, was built in 1818–1820 and 1845–1852 between Vytegra River in the east and Svir River in the west. The canal was part of the Mariinsk Canal System, a forerunner of the Volga–Baltic Waterway, and aimed to create a quiet pass for boats avoiding the stormy waters of the lake. It is around wide, and lies between and from the shores of the lake. The canal is not used for active navigation at present. There are about 1650 islands in the lake with