St Lawrence Seaway

Deep-water channel and transport corridor in North America, connecting the St Lawrence River with the Great Lakes, allowing ocean-going vessels to navigate from the Atlantic Ocean to Lake Superior (3,769 km/2,342 mi). It was opened for navigation by the USA and Canada in 1959.

In the strict sense the seaway is the section from Montréal to Lake Ontario, but the name is applied generally to the whole system from the Atlantic to the Great Lakes. There are 78 ports on the seaway, which remains navigable for moderate-sized vessels for about 250 days a year.

The international boundary between Canada and the USA runs along the river and through lakes Ontario, Erie, Huron, and Superior, and the St Lawrence Seaway project was undertaken jointly by the USA and Canada. The preliminary works on the seaway on the Canadian side of the river began in 1954, although the scheme had been envisaged some years earlier. The main operations involved were the deepening of the Welland Canal (which allows ships to bypass the Niagara Falls) to 8.2 m/27 ft over 16 km/10 mi of its length, the dredging of lakes St Francis, St Clair, and St Louis, the rebuilding of the Lachine Canal (circumventing the Lachine Rapids) with two locks, and the construction of seven locks between Montréal and Lake Ontario, eight in the Welland Canal, and one at Sault Sainte Marie, between lakes Huron and Superior.

In 1951 the Canadian parliament agreed to undertake the construction of the seaway in Canadian territory; the Ontario Hydroelectric Commission and an authority appointed by the US government were entrusted with the power development of the International Rapids section. In 1953 a 50-year permit was granted by the US Federal Power Commission to the energy authority of the state of New York to develop the US share of the power project in the International Rapids section. Work on the hydroelectric development started in 1954.