Look up the laws on “adverse possession.” They may be able to refute the government’s claim.
IMO, the Lake of the Ozarks is a hell hole. But, different strokes for different folks. Some people like the place. People have been building right up to the water’s edge for generations. That’s what you do at the Lake of the Ozarks. For the government to come along now and say, “Sorry, you can’t do that,” is nuts. Somebody needs to invite a few federal bureaucrats down for a fact finding mission . . . down a lonely deserted cove, if you can find one.