What can we do about a new neighbor typing a cable to our cherry tree that the post is in for our property line?

This guy also claimed to own part of our yard where our apple trees and pond are. we proved thru the stake in the tree he was wrong. Now he has dug himself a pond. Tapped into the underground spring that fed our pond/We have cat tails and had salamanders, frog, and turtlet may not have been deep but here more than 20 years. We want our watr back I