It is unlawful for any person, firm or corporation to enter or go upon the watershed of the city of Aberdeen, as the same is defined in Section 13.36.010, for any purpose whatsoever; provided, that this section shall not apply to authorized officials, employees or agents of the city of Aberdeen engaged in city business, officers authorized to enforce this chapter, nor to the owners of the land and their authorized employees who enter the area for purposes of inspection and control.