While owning the bank is great, you only need to own a square foot of it to use the whole pond. Owning more of the pond bottom does not usually come with benefits. You just have to hope for a good neighbor. If things ever get that bad, it might be permissible for you to drain the pond (if the dam is on you property), and then push up dirt within your property to wall it off from the cove creating separate ponds. Hopefully it will not ever come to that.
