When a highway leading to a public ferry over a river which is the boundary line between two counties, is subject to inundation and flood damage, such highway in either or both of such counties may be constructed, repaired or maintained by the adjoining counties, or either of them, or may be partly constructed, repaired or maintained by both or either of such counties.
     The county boards of such adjoining counties may enter into a contract as to the proportion of the expense of construction, repair or maintenance to be borne by each, and such contracts shall be judicially enforceable; or either county may construct or maintain, or assist in the construction and maintenance of such highway in either or both counties.