Britannica Sources used in this answer

Which two countries jointly built the St. Lawrence Seaway?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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 St. Lawrence Seaway was built jointly by Canada and the United States.1

Although the project was long pursued by Canada, the United States was initially a reluctant partner, with the U.S. Senate rejecting an earlier treaty in 1932. Following years of delay, the United States finally approved participation in the project in 1954, largely due to the prospect of Canada proceeding independently. The completed waterway, which opened in 1959, provides a deep-draft route from the Atlantic Ocean to the Great Lakes, significantly impacting North America's industrial and agricultural transport.21