Waterfront home owners have what is called Riparian Rights. Basically they are deeded the land under the water but can't really do anything with it. We see it all the time when new people move to a lake and think they own the water. I live on a public lake and this comes up almost every year when boats anchor or cruise close to shore. We have had the DNR and local water patrol called. Never had the officer side with the homeowner.
Here is some reading that explains it.
https://en.wikipedia.org/wiki/Riparian_water_rights