46 U.S.C. § 55334

1. (a)Except as provided in subsection (b), an American Great Lakes vessel may not be used to—
   1. (1)engage in trade—
      1. (A)from a port in the United States that is not located on the Great Lakes; or
      2. (B)between ports in the United States;
   2. (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. (3)provide a service (except ocean freight service) as—
      1. (A)a contract carrier; or
      2. (B)a common carrier on a fixed advertised schedule offering frequent sailings at regular intervals in the foreign trade of the United States.
2. (b)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.