Seawaymax lake freighters often ply the Saint Lawrence Seaway. The Saint Lawrence Seaway and Great Lakes Waterway opened the Great Lakes to ocean-going vessels. It forms a key section of the St. Lawrence Seaway and Great Lakes Waterway. Lawrence Seaway (via Lake Michigan) and the Inland Waterway System (via the Ohio River). Shipping on the Saint Lawrence Seaway was superseded by trucking on highways. Navigation downstream is provided by the Welland Canal, part of the Saint Lawrence Seaway. The 1959 opening of the Saint Lawrence Seaway adversely affected NYC freight business. The Saint Lawrence Seaway, completed in 1959, opened the Midwest to the Atlantic Ocean. Commercial vessel transit information is hosted on the U.S. Saint Lawrence Seaway Development Corporation website. The Saint Lawrence Seaway was preceded by several other canals. The region also has significant maritime infrastructure being on the Great Lakes-Saint Lawrence Seaway system. There are seven locks in the Saint Lawrence River portion of the seaway. If assigned by the St. Lawrence Seaway Authority. Chicago became an ocean port with the opening of the Saint Lawrence Seaway in 1959. This river provides the basis for the commercial Saint Lawrence Seaway.