Well, where does a wide spot in a marshy river end and a lake begin? That's the problem ... in Florida, the elevation is so low that a few inches rise or fall in the lake can make miles of shoreline appear or disappear. If you zoom in and out on Google Maps, you can see that when the resolution in the map data changes, the height of the lake changes dramatically. Zoom out far enough, and the lake is full. Get close, and it turns into this thing that looks more like a river delta than a lake.
I have seriously toyed with the idea of putting a puzzle cache there ... but getting permission and, well, just getting there are making that pretty much too difficult to bother with.