In my neck of the woods, rivers, streams, lakes, etc. are "public waters" regardless of how much of the shoreline may be owned by private citizens. The typical setback for public waters is 75', but can be as little as 50' if you're really luck and as much as 150' if you're unlucky and have an "environmental" water.
This past weekend I was in a different part of the woods. I was informed, by people in the know, that there are lakes where you can build a boathouse right over the water. Some creeks/rivers have a 30' setback from its centerline. This means in some instances you can build right at the shoreline (but not alter the shoreline).
Why for come the water is different in one state in a different state? Why for come it's OK in that state to build right next to the water, but in this state we'll completely destroy the ecosystem if we get closer than 50'?