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 Ladoga were connected by a strait or a river outlet at least until the formation of the River Neva, and possibly even much later, until the 12th century AD or so. At 9,500 BP, Lake Onega, previously draining into the White Sea, started emptying into Ladoga via the River Svir. Between 9,500 and 9,100 BP, during the transgression of Ancylus Lake, the next freshwater stage of the Baltic, Ladoga certainly became part of it, even if they hadn't been connected immediately before. During the Ancylus Lake subsequent regression, around 8,800 BP Ladoga became isolated. Ladoga slowly transgressed in its southern part