At Warren Dunes State Park, they have a park naturalist (that's him in the hat) that shared with the beach goers about the dunes, the reason for the fog the day before, and about fossils.
That's right. There are coral fossils in Lake Michigan, and if you know what you are looking for, you can find them. This day was particularly good for fossil hunting because there was hardly a ripple on the water. The air was barely moving, no waves to speak of, and it was HOT. There wasn't much else to do but sit in the water.