Take plenty of pictures Rox. If he is breaking the law and the DEP knows about it and has proof, the state will force him to return the area back to it's original condition at HIS expense.

Now to take his side. His property deed probably states he owns up to waters edge so probably he does own it until it fills back in.
To compel a man to subsidize with his taxes the propagation of ideas which he disbelieves and abhors is sinful and tyrannical. Thomas Jefferson