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 Historical, Architectural and Ethnographic Preservation Area. There are 89 wooden architectural monuments of the 15th to 20th centuries on the island. The most remarkable of those is Kizhi Pogost of the early 18th century which consists of a summer church with 22 domes, a winter church with nine domes, and a belfry. The pogost was included in the list of UNESCO World Heritage sites in 1990. In the summer, there are daily boat connections to the island from Petrozavodsk. Another attraction of the lake are the Onega petroglyphs (rock engravings). They are located on the eastern coast of the lake