A seaport listed in s. 403.021(9)(b) is authorized to provide for onsite or offsite stormwater treatment for water quality impacts caused by a proposed port activity that requires a permit and that causes or contributes to pollution from stormwater runoff. Offsite stormwater treatment may occur outside of the established boundaries of the port, but must be within the same drainage basin in which the port activity occurs. A port offsite stormwater treatment project must be constructed and maintained by the seaport or by the seaport in conjunction with an adjacent local government. In order to limit stormwater treatment from individual parcels within a port, a seaport may provide for a regional stormwater treatment facility that must be constructed and maintained by the seaport or by the seaport in conjunction with an adjacent local government.