Is there any possibility that the upstream owner has engaged in contributory negligence in this matter by failing to properly clear the various wood and material sources from the creek area which were subseqently used by the beavers in their construction?

  I would draw a parallel to clearcutting hazzardous, dry grass in high fire-danger areas, or removing dead tree limbs that hang over easement roads that could fall and kill someone.   In either case in Western law, the liability on the property owner for damages caused which could have been avoided appears high.  Perhaps a similar theory could be brought forth in this instance?  Ideas?