When it is determined that any existing or proposed dam or obstruction requires a fishway and none has been installed therein, the director shall keep the same open until said fishway is put therein by the owner. Where a fishway has heretofore been constructed and approved by the director and has proved useless or inadequate for such purpose, the director shall have authority to construct a new fishway and to pay the expense of such construction out of the fish and game fund. However, when such fishway is then properly functioning, it shall be maintained and replaced as required at the expense of the person owning the dam or other obstruction.