The board of any town or county that is bounded in part by a river or a highway that is also a state boundary line may enter into an agreement with any adjoining municipality or county in the other state for the maintenance, construction, and reconstruction of boundary line highways and bridges. The costs shall be apportioned by agreement.
Wis. Stat. § 82.28
2003 Wis. Act 214, which affected this section, contains extensive explanatory notes.