Just a simple thought, for sure not the whole situation discussed by me,  but for the sake of discussion I would start with this, 1st.; a creek meandering through a property is a natural thing, which proceeds naturally on  it's own course and that course should only be changed by a natural Occurance when it is diverted or slowed or stopped. 2nd; beavers are animals of nature and it is there nature to dam water to aid in  there natural daily needs, they do not build dams on  permit or license, but  naturally.

Seems to me Brian as no cause of action against Chris, he has an issue with the beavers. It also seems to me Chris is not obligated to destroy the beaver dam to acommediate Brian and the restoration of creek flow.. 

The next obvious question is wether Brian looses value due to the creek flow lose, or just natural changes caused by the lack of water. 

Yea, i see now a can of worms being open, i have all kinds of things popping-up for consideration now. Later.