Opened to deep draft navigation in 1959.
Lock systems:
Montreal to Lake Ontario - 2 U.S., 5 Canadian
Welland Canal - 8 Canadian
St. Mary's River - 4 U.S. parallel locks -- one transit (Army Corps of Engineers)

Vessel maximum: 225.5 m (740 ft.) length; 23.7 m (78 ft.) beam; 8.0 m (26 ft., 3 in.) draft; 35.5 m (116.5 ft.) height above water.

Channels maintained at 8.2 m (27 ft.) minimum over the chart datum.

Distance from the Atlantic Ocean to Duluth, Minnesota on Lake Superior = 2,038 nautical miles (2,342 statute miles or 3,700 kilometres), 8.5 sailing days. Includes some 245,750 square kilometres (95,000 square miles) of navigable waters.

Sailing time (normal conditions) between certain ports on the Great Lakes and the intersection of the Seaway ship channel and Montreal Harbor, using an average sailing time of 12 mph (10.4 knots)

• Port authority