U.S.-Canadian waterway and lock system.
Located along the upper Great Lakes . Its construction, carried out in 1954–59, involved clearing a 186-mi (299-km) stretch of the St. Lawrence River between Montreal and Lake Ontario . It included lakes, rivers, locks, and canals that extended for 2,340 mi (3,766 km) to connect Duluth, Minn., with the head of the Gulf of {{link=Saint Lawrence, Gulf of">St. Lawrence . With the Great Lakes, it provides 9,500 mi (15,285 km) of navigable waterways. It allows deep-draft ocean vessels access to the Great Lakes' rich industrial and agricultural regions. It is navigable from April to mid-December.