Agreed. If they are fording, it's not navigable. They must approach and depart through the navigable water ways. If they are doing anything different, it's not legal. But I have seen people attempt to illegally come up shorelines, trespassing, and claiming they have a right to enter. Which isn't the case. There isn't enough details to really understand what's going on in this case. Details matters as we're already cutting hairs to describe possibilities.