Negative consequences of possible level variations in the Neva Bay by the end of the century due to the age-old level rise and extreme storm surges for St. Petersburg are discussed. These include flooding, submergence, erosion of shores and bogging of coastal areas. It is shown that the most realistic forecast of the level in Kronstadt by the end of the century is its rise up to 34–59 cm BS (the Baltic system of heights), and according to the “pessimistic” forecast there is a possibility of its rise to 80– 90 cm BS. In this case, significant areas of the Admiralteysky, Vasileostrovsky, Kirovsky and Petrogradsky city districts will be flooded. The results of assessing the flood zone boundaries of the city’s territory for one-percent water levels are given. In case of extreme storm surges, the possible level rise north of Gorskaya may amount to 600 cm BS. Especially the effect of flooding caused by storm surges is pronounced near Sestro-retsk. At an altitude of the 4-m surge wave the total area of possible flooding of Kurortny district exceeds 1260 hectares, all the beaches being completely lost.