Whether you can actually swim is another story. As a kid on the North Shore, I found August the one and only time we could splash around in the water. It wasn't really swimming, but we'd get mostly all wet. My favorite thing to do was to find a ledge of rock with secure seating but still exposed to the waves. We'd let two-foot waves roll in and wash over us as we clung to cracks in the rocks.
Now, as a resident of Duluth with a sandy backyard, I'm glad to know that my kids can swim and not get rashes or diarrhea from the water.