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How did the St. Lawrence Seaway change Canada’s iron ore trade with the United States?

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Map showing the St. Lawrence hydrographic system and the five main sectors of the St. Lawrence Seaway project, stretching from Lake Ontario near Kingston through various locks, canals, and dams along the Canada-United States border to Montreal. The map highlights key locations such as the Thousand Islands, International Rapids, Lake St. Francis, Soulanges, and Lachine sections, with detailed labeling of major locks, canals, and power dams. Cross sections of the lock and canal system are depicted — St. Lawrence Seaway The St. Lawrence hydrographic system, with the five main sectors of the St. Lawrence Seaway project.

The construction of the St. Lawrence Seaway fundamentally transformed the iron ore trade between Canada and the United States. Prior to the opening of the seaway, Canada was an importer of American iron ore. Following its completion, Canada became a major exporter of the commodity to the United States, driven by the discovery of vast iron deposits in Quebec and Labrador that were essential for American steel mills.21

This shift facilitated efficient two-way trade, largely supported by specialized vessels known as lakers. These ships are designed to navigate the seaway's locks, allowing them to transport grain from the Great Lakes to world markets and return with Canadian iron ore loaded in the lower St. Lawrence region. Today, iron ore remains the second largest commodity moved through this vital international trade route.21