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The Great Lakes-St. Lawrence Seaway System

May 8, 2017

The Great Lakes-St. Lawrence Seaway is a deep draft waterway extending 3,700 km (2,340 miles) from the Atlantic Ocean to the head of the Great Lakes, in the heart of North America. The St. Lawrence Seaway portion of the System extends from Montreal to mid-Lake Erie. Ranked as one of the outstanding engineering feats of the twentieth century, the St. Lawrence Seaway includes 13 Canadian and 2 U.S. locks.

The Great Lakes and St. Lawrence River have been major North American trade arteries since long before the U.S. or Canada achieved nationhood. Today, this integrated navigation system serves mariners, farmers, factory workers, and commercial interests from the western prairies to the eastern seaboard.

Virtually every commodity imaginable moves on the Great Lakes Seaway System. Annual commerce on the System exceeds 200 million net tons (180 million metric tons), and there is still ample room for growth. Some commodities are dominant:

  • Iron ore for the steel industry
  • Coal for power generation and steel production
  • Limestone for construction and steel industries
  • Grain for overseas markets
  • General cargo, such as iron and steel products and heavy machinery
  • Cement, salt and stone aggregates for agriculture and industry

Up-to-date information about the Seaway is available within the SLSDC System Brochure

Lock Systems

All of the 15 U.S. and Canadian Seaway locks have the following dimensions:

  • Attracting vessels 227.7 meters (740 feet) in length to transit
  • Attracting vessels 24 meters (78 feet) in width to transit
  • Attracting vessels 8.9 meters (26 feet and 6 inches) in depth to transit


Montreal to Lake Ontario (2 U.S. and 5 Canadian locks, listed east to west)

  • St. Lambert (Canadian)
  • Cote St. Catherine (Canadian)
  • Upper Beauharnois (Canadian)
  • Lower Beauharnois (Canadian)
  • Snell (U.S.)
  • Eisenhower (U.S.)
  • Iroquois (Canadian)

Welland Canal (8 Canadian Locks)

Updated: Wednesday, December 31, 2014
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