Looking at this picture, and reading what the article described as to the law in Missouri, it seems to my feeble mind that the small trees at the edge of the river bank and along the sand bar are probably within the easement, but the woods beyond those trees are not. That is what is probably confusing to people, because the exact line is indefinite, and we as property owners usually like to have a boundary.
Another confusion you may have is regarding the legal definition of navigible. You see, in Missouri, navigable does not mean the same as in the Delaware River or the Hudson. A canoe that can make its way down most of the year probably makes a river navigable. A creek that only has running water after a storm is not.
The picture also makes it appear as though the guy who was shot was shot out in the middle of the sand bar. If he shot the guy there, it's a jail he'll be goin'. The easement is definitely going to extend onto that sand bar. Which means he acosted people who had a right to be where they were. Unless your knowledge of Missouri case law indicates otherwise, in which case, I am happy to hear your legal argument.
I’ll ask you:
Right or wrongly you confront trespassers on your property they refuse to leave and appear they have had plenty to drink. One of the group grabs a rock and starts towards you a second member of the party grabs your arm. Do you shoot?
Also I did read the article and no one interviewed stated 100% were the property line is. In fact the everyone interviewed in the article gave the opinion was that it was a very gray area.
That said with your 100% for sure knowledge of Missouri law it seems to me that you are the one that should have been interview.