Every owner or occupier of a dam over which a state highway passes shall keep such dam in good order, at least 12 feet wide at the top, and also keep in good order the substructure of a bridge of like width over the pier heads, floodgates, or any wastecut through or around the dam, provided that when these requirements have been met, the superstructure of any such bridge shall be maintained by the Commissioner of Highways. The Commissioner of Highways shall inspect all such bridges and report any needed repairs to the owner in writing. If such owner fails to comply with the provisions of this chapter, he is guilty of a misdemeanor punishable by a fine of $2 for every such failure of 24 hours. However, if a milldam is carried away or destroyed by flood or any other extraordinary natural cause, the owner or occupier thereof shall not be subject to such fine until one month after any mill operated in whole or in part by water impounded by such dam has been put into operation by such waterpower.