46 U.S.C. § 55334

(a) Prohibitions .— Except as provided in subsection (b), an American Great Lakes vessel may not be used to— (1) engage in trade— (A) from a port in the United States that is not located on the Great Lakes; or (B) between ports in the United States; (2) transport bulk cargo (as defined in section 40102 of this title ) that is subject to section 55305 or 55314 of this title or section 2631 of title 10 ; or (3) provide a service (except ocean freight service) as— (A) a contract carrier; or (B) a common carrier on a fixed advertised schedule offering frequent sailings at regular intervals in the foreign trade of the United States. (b) Off-Season Exception .— An American Great Lakes vessel may be used for not more than 90 days during any 12-month period to engage in trade prohibited by subsection (a)(1)(A), except during the Great Lakes shipping season.