I used to live on a river in Wisconsin and there the rule is land that goes from the actual river's edge to the OHWM (Ordinary High Water Mark) is not directly owned by the property owner...it is public  property (although you can mow it and maintain it like it was yours).  Thus, on a flowing river, I could walk the shoreline between the OHWM and the actual waterline and not be trespassing.

My dad had told me it was a federal law, but looking at

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it seems it was just a state law.