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Saint Lawrence Seaway

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The Eisenhower Locks in Massena, NY.

The St. Lawrence Seaway is the common name for a system of canals that permits ocean-going vessels to travel from the Atlantic Ocean to the Great Lakes, as far as Lake Superior. Legally it extends from Montreal to Lake Erie, including the Welland Canal and the Great Lakes Waterway. The seaway is named after the Saint Lawrence River, which it follows from Lake Ontario to the Atlantic Ocean.


The Saint Lawrence Seaway was preceded by a number of other canals. In 1862, locks on the St Lawrence allowed transit of vessels 186 feet (57 m) long, 44½ feet (13.6 m) wide, and 9 feet (2.7 m) deep. The Welland Canal at this time allowed transit of vessels 142 feet (43 m) long, 26 feet (7.9 m) wide, and 10 feet (3.0 m) deep. These were generally too small to allow passage of larger ocean-going ships.

Proposals for the Seaway started in 1909, but was 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. The Seaway opened in 1959 and cost $470 million US dollars, $336.2 million of which was paid by the Canadian government.

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.

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 766 feet (233.5 m) long, 80 feet (24 m) wide, and 30 feet (9.1 m) deep. The maximum allowed vessel size is slightly smaller: 740 feet (225.6 m) long, 78 feet (23.8 m) wide, and 26 feet (7.9 m) 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 down the seaway to the ocean. The only lock on the Great Lakes Waterway is 1,200 feet (357 m) long, 110 feet (33.5 m) wide and 32 feet (9.8 m) deep, but the channels are not kept that 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 41 feet (12.5 m) ( panamax depth) downstream of Quebec City, 35 feet (10.7 m) between Quebec City and Deschaillons, 37 feet (11.3 m) to Montreal, and 28 feet (8.2 m ) upstream of Montreal. Channels in the Great Lakes Waterway are slightly shallower: 25 to 27 feet (7.62 to 8.2 m). In the late 1990s the seaway has been deepened and widened increasing near panamax sized ship access upstream from the Atlantic ocean to 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.

Environmental effects

To create a navigable channel through the Long Sault rapids and to allow hydroelectric stations to be established immediately upriver from Cornwall, Ontario and Massena, New York, an artificial lake had to be created. Called Lake St. Lawrence, it required the flooding on July 1, 1958 of ten villages 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, including the sea lamprey and the zebra mussel, into the Great Lakes Basin. These organisms were introduced via ballast water from oceanic vessels.

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 130 ft.). Surprisingly, the water temperature can be as warm as 70°F with little or no thermocline during the mid to late summer months.

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