Marinas and gas docks have since discontinued the use of
"Styrofoam" material for flotation. Gasoline and oil
film on the water surface eventually dissolves the Styrofoam at the waterline and periodically has to be replaced. Floating docks are now supported by hollow plastic, and sometimes cast concrete tubs which last much longer and are easier to clean. Styrofoam has very little strength and had to be "boxed" in/confined.
NB