As someone who has owned a Seaplane for several years and flown it all
over USA, Canada and Alaska, I can tell you it is not as simple as
"Feds retain juridiction over all navigable waterways". What is
navigable? What is a vessel? There are many, many, many waterways
where boating and recreation are under state, county, city or some
other entity's control other than the "Feds". And they are waterways
being navigated, so in some sense, they are navigable.

Now Lake Michigan being a large, obviously commercially navigable
waterway, I am sure the Coast Guard has juridiction over much of it.
But it also lies in numerous states and there are numerous harbor
authorities that come into play, cities, counties, parks, who knows
what all?