N.H. Rev. Stat. Ann. § 473:7

The fence-viewers, upon application of either party, shall view any brook, river, pond, creek or ditch alleged not to be equivalent to a legal and sufficient fence, and, if they judge it to be not so equivalent, shall make a division of the fence, and, if it is impracticable to build it on the boundary line without unreasonable cost, shall determine where it shall be located, and shall give notice to the parties to build it according to such division and location within a time by them limited.