Michigan Compiled Laws, Chapter 324. Natural Resources and Environmental Protection § 324.80198a

Sec. 80198a. (1) When wind conditions on the Great Lakes attain a magnitude whereby 1/3 of the waves resulting from the conditions cause any public dock, pier, wharf, or retaining wall to be awash, it constitutes a state not conducive to the orderly and safe use and occupancy of those structures.

(2) When the conditions described in subsection (1) exist, any harbormaster, peace or police officer, or other authorized official may rope off or barricade entry to these structures or post in a conspicuous manner notices that entry on those structures for the purpose of fishing, swimming, or other recreational activity is prohibited.

(3) A person shall not knowingly enter or remain upon any public dock, pier, wharf, or retaining wall for the purpose of fishing, swimming, or other recreational activity when the structure is roped, cabled, or otherwise barricaded in a manner designed to exclude intruders, when notice against entry is given by posting in a conspicuous manner, or when notice to leave or stay off is personally communicated to that person by a peace or police officer or other authorized official of the local unit of government.