53 Pa. Stat. § 16871
That it shall be lawful for the councils of said city to provide, by ordinance, for the cleaning of the docks on the Delaware and Schuylkill front of said city, and to require the owners of wharves and piers, which surround such docks, to cleanse the same; and after thirty days' default from the service of notice on them to perform said duty, it shall be lawful for the city to do said work, and to apportion the expenses thereof among the owners of the wharves and piers adjoining, in proportion to the extent of their wharves, having the privilege or use of such docks, and to collect the same by filing liens therefor and process thereupon as in case of claims for paving: Provided, That no dock shall be cleansed to a greater depth than the natural bed of the river.
53 P.S. § 16871