To amend the Merchant Marine Act, 1936, to preserve the percentage of certain agricultural commodities exported from Great Lake ports.

Amends the Merchant Marine Act, 1936 to extend indefinitely, with regard to certain cargo preference provisions, the requirement that the Secretary of Transportation take steps to preserve for shipment through the Saint Lawrence Seaway the percentage share, or metric tonnage of bagged, processed, or fortified commodities experienced in calendar year 1984, of waterborne cargoes exported from Great Lakes ports pursuant to specified provisions of the Agricultural Trade Development and Assistance Act of 1954.