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Why did the U.S. Army Corps of Engineers deepen the Straits of Mackinac for the St. Lawrence Seaway?

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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 premise that the U.S. Army Corps of Engineers deepened the Straits of Mackinac specifically for the St. Lawrence Seaway is accurate in the context of the broader project requirements.

The U.S. Army Corps of Engineers performed this work to make the seaway operational by ensuring that the connecting channels between the Great Lakes could accommodate deep-draft ocean vessels. By deepening the Straits of Mackinac, as well as the St. Marys River, the Detroit River, Lake St. Clair, the St. Clair River, and various harbours, the project successfully created a continuous, deep-water navigation system that linked the industrial and agricultural heartlands of North America to the Atlantic Ocean.12