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What role do the Thousand Islands play in the St. Lawrence Seaway route?

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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 Thousand Islands section of the St. Lawrence River serves as a critical segment of the St. Lawrence Seaway. During the construction of the seaway, which aimed to create a deep-draft navigation channel, the United States government was responsible for clearing shoals from this area to ensure safe passage for large vessels.1

By removing these underwater navigational hazards, authorities were able to help establish a consistent waterway depth of 8.2 metres (27 feet) throughout the route, facilitating modern maritime traffic between the Great Lakes and the Atlantic Ocean. Aside from this navigational role, the Thousand Islands are a group of more than 1,500 islands spanning the border between New York, U.S., and Ontario, Canada, and are widely recognized as a traditional recreational area.1234