Actually more effective than is generally known.
Baltic Sea fleet was bottled up in Leningrad, but ship's guns were used as heavy artillery.
Black Sea fleet was quite active, from amphibious landings in the Crimea in 1941, support (supply) of the defenders in Sevastopol.
Since the Turks would not let Axis into the Black Sea the Soviet naval forces were superior, and kept the Axis from threatening Black Sea coastal areas