 Around 5,000 BP the waters of the Saimaa Lake penetrated Salpausselkä and formed a new outlet, River Vuoksi, entering Lake Ladoga in the northwestern corner and raising its level by 1–2 m.

The River Neva originated when the Ladoga waters at last broke through the threshold at Porogi into the lower portions of Izhora River, then a tributary of the Gulf of Finland, between 4,000 and 2,000 BP.Dating of some sediments in the northwestern part of Lake Ladoga suggests it happened at 3,100 radiocarbon years BP (3,410–3,250 calendar years BP).The Ladoga is rich with fish.