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What is Lake St. Lawrence and how was it created?

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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.

Lake St. Lawrence is a 48-km (30-mile) long reservoir that serves as an expansion of the St. Lawrence River located west-southwest of Cornwall, Ontario.12

It was created during the construction of the St. Lawrence Seaway in the 1950s. To harness the river's hydroelectric power potential, engineers constructed the Iroquois Control Dam and the Moses-Saunders Power Dam in the International Rapids section of the river. The resulting impoundment of water formed the lake, which began generating power in July 1958. The project was a massive undertaking that required the relocation of approximately 6,500 people from riverside communities to accommodate the new waterway.13