Wis. Stat. § 30.122: Unauthorized structures.

All permanent alterations, deposits or structures affecting navigable waters, other than boathouses, which were constructed before December 9, 1977 and which did not require a permit at the time of construction, shall be presumed in conformity with the law, unless a written complaint is filed within 180 days of December 9, 1977. Upon the filing of a complaint, the department shall proceed with an action to enforce the applicable statutes.