I had the same problem. Here is what worked for me: First, blast as much of the growth away with a high pressure hose as you can. After you do this, turn the inflatable bottom side up and let it dry in the sun for several days. If the several day time frame does not work for you, strap the dingy bottom side up to the top of your car and drive around with it for a while. This will cause the growth to dry up and will be very easy to get off with a soft scrub pad or stiff bristle brush. Good luck.