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The St. Lawrence Seaway (French: la Voie Maritime du Saint-Laurent) is the common name for a system of locks, canals and channels that permits ocean-going vessels to travel from the Atlantic Oceanmarker to the North American Great Lakesmarker, as far as Lake Superiormarker. Legally it extends from Montrealmarker to Lake Eriemarker, including the Welland Canalmarker. The seaway is named after the Saint Lawrence Rivermarker, which it follows from Lake Ontariomarker to the Atlantic Ocean. This section of the seaway is not a continuous canal, but rather comprises stretches of navigable channels within the river, a number of locks, and canals made to bypass rapids and dams in the waterway.


The Saint Lawrence Seaway was preceded by a number of other canals. In 1862, locks on the St Lawrence allowed transit of vessels long, wide, and deep. The Welland Canal at that time allowed transit of vessels long, wide, and deep, but was generally too small to allow passage of larger ocean-going ships.

Proposals for the seaway started in 1909, but were met with resistance from railway and port lobbyists in the US. In addition to replacing the canal system, generation of hydroelectricity also drove the project. After rejecting numerous agreements to construct a seaway, construction was approved in 1954 when Canada declared it was ready to proceed unilaterally.

In the United States, Dr. N.R. Danielian was the Director of the 14 volume St. Lawrence Seaway Survey in the U.S.marker Department of Commercemarker (1939-1943), worked with the U.S. Secretary of State on Canadian-United States issues regarding the Seaway and worked for over 15 years on passage of the Seaway Act. He later became President of the Great Lakes St. Lawrence Association to further the interests of the Seaway development to benefit the American Heartland.

The seaway opened in 1959 and cost US$470 million, CAD$336.2 million of which was paid by the Canadian government. Queen Elizabeth II and President Dwight D. Eisenhower formally opened the Seaway with a short cruise aboard Royal Yacht Britanniamarker after addressing the crowds in St. Lambertmarker, Quebecmarker.

The seaway's opening is often credited with making the Erie Canal obsolete, thus setting off the severe economic decline of several cities in upstate New York.

Locks in the Saint Lawrence River

There are seven locks in the Saint Lawrence River portion of the Seaway. From downstream to upstream they are:

  1. St. Lambert Lock - Saint Lambertmarker, QCmarker
  2. Côte Ste. Catherine Lock - Sainte-Catherinemarker, QC
  3. Beauharnois Locks (2 locks) - Melochevillemarker, QC
  4. Snell Lock - Massenamarker, NYmarker
  5. Eisenhower Lock - Massenamarker, NY
  6. Iroquois Lock - Iroquoismarker, ONmarker

Locks in the Welland Canal

There are 8 locks on the Welland Canalmarker.

Lock and channel dimensions

The size of vessels that can traverse the seaway is limited by the size of locks. Locks on the St Lawrence and on the Welland Canal are long, wide, and deep. The maximum allowed vessel size is slightly smaller: long, wide, and deep; many vessels designed for use on the Great Lakes following the opening of the seaway were built to the maximum size permissible by the locks, known informally as Seaway-Max. Large vessels of the lake freighter fleet are built on the Lakes and cannot travel downstream beyond the Welland Canal. On the remaining Great Lakes, these ships are constrained only by the largest lock on the Great Lakes Waterway, the Poe Lock at the Soo Locksmarker, which is long, wide and deep.

Water depth is another obstacle to vessels, particularly in connecting waterways such as the St. Lawrence River. The depth in the channels of the seaway is (Panamax-depth) downstream of Quebec Citymarker, between Quebec City and Deschaillonsmarker, to Montreal, and upstream of Montreal.

Channel depths and limited lock sizes mean that only 10% of ocean-going ships can traverse the entire seaway. Proposals to expand the seaway, dating from as early as the 1960s, have been rejected as too costly, and environmentally and economically unsound. Lower water levels in the Great Lakes have also posed problems for some vessels in recent years.

While the seaway is currently (2008) mostly used for shipping bulk cargo, the possibility of its use for large-scale container shipping is under consideration as well. If the project goes ahead, feeder ships would take containers from the port of Oswegomarker on Lake Ontario in upstate New Yorkmarker to Melford International Terminalmarker in Nova Scotiamarker for transfer to larger ocean-going ships.

Environmental effects

To create a navigable channel through the Long Sault rapids and to allow hydroelectric stations to be established immediately upriver from Cornwall, Ontariomarker and Massena, New Yorkmarker, an artificial lake had to be created. Called Lake St. Lawrence, it required the flooding on July 1, 1958 of six villages and three hamlets in Ontario, now collectively known as "The Lost Villages". There was also inundation on the New York side, but no communities were affected.

The creation of the seaway also led to the introduction of foreign species of aquatic animals, most notably the zebra mussel into the Great Lakes Basin.

The seaway provides significant entertainment and recreation such as boating, camping, fishing, and scuba diving. Of particular note is that the seaway provides a number of divable wrecks within recreational scuba limits (shallower than ). Surprisingly, the water temperature can be as warm as with little or no thermocline during the mid to late summer months.


  1. Great Lakes St. Lawrence Seaway System Map, accessed 2009-07-05
  2. "Oswego Considered For Major Container Port: Plan calls for $3M facility to create first Great Lakes site handling global container shipments", by John Doherty. Wednesday, October 22, 2008


  • Seaway Handbook issued by the St. Lawrence Seaway Management Corporation, (Head Office, 202 Pitt Street, Cornwall, Ontario, Canada K6J 3P7) 2006.
  • (Worldcat link: [4435])

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