This is what we have on Minnetonka. If you don't paint, you will get slime/algae on the waterline and you will get Zebra Mussels. Hell ya get slime on the waterline no matter what so ya motor out in to the bay and hop in the water to scrub it off. People who do not paint their boats have their boats on lifts. The lifts get covered with them and need to be scrapped or just pulled and cleaned. This is the nature of our lake.Some freshwater lakes are heavily infested with zebra mussels. They are prolific and will heavily foul a boat. In other areas there is a lot of algae that will start as slime and over the course of a season turn into a full waterline beard.