The State of Canada's Environment — 1996 Chapter 6 — Great Lakes–St. Lawrence Basin Overview of Human Activities and Environmental Issues Physical restructuring The St. Lawrence Seaway–Great Lakes Waterway

The St. Lawrence Seaway–Great Lakes Waterway

In the early 1800s, several obstacles prevented ships from reaching the Great Lakes from the ocean. Several series of rapids prevented ships from reaching Lake Ontario from the St. Lawrence River, and Niagara Falls formed a barrier to Lake Erie. Further, the rapids at Sault Ste. Marie blocked access to Lake Superior. Canals and locks were built to allow small vessels to bypass these obstacles. In 1824, the Lachine Canal was opened, bypassing the rapids in front of Montreal, and in 1845, the first Beauharnois Canal allowed ship passage past the Soulanges Rapids west of Montreal. The Welland, Rideau, Trent–Severn, and other canals opened direct water routes to the interior.

The current Seaway system, built jointly by Canada and the United States between 1954 and 1959, consists of the open waters of the Great Lakes and St. Lawrence together with all the linking canals, locks, dams, control structures, and harbours. In the St. Lawrence section alone, seven locks were built and 87 million cubic metres of material excavated (Lasserre 1980). During the same period, the shipping channel between the estuary and the first lock at Montreal was deepened and widened. More than half of this 370-km stretch of the St. Lawrence had to be dredged. The project changed both the landscape and the social fabric of the flooded area along portions of the St. Lawrence River. For example, an estimated 6 500 Canadians were relocated to accommodate the navigation and power pool upstream of the Moses–Saunders dam at Cornwall, for which flooding extended 60 km upstream (Ontario Great Lakes/Seaway Task Force 1981).

Large vessels (up to 222 m long) can now reach the Great Lakes. Grain, iron ore, coal, and limestone comprise 85% of the freight, most of which travels between ports within the system. The total economic impact of the Seaway system on the Canadian economy is estimated to be $2–4 billion annually (Sub-Committee on the St. Lawrence Seaway 1994). More than 200 million tonnes of cargo move on and through the Seaway each year. Over the past two decades, however, the volume of traffic and cargo has declined (see the " St. Lawrence Lowlands ecoregion" section of this chapter).

Significant drops in elevation in various sections make the St. Lawrence River ideal for electric power production. The first hydroelectric generating facilities, built by private firms in the late 1800s, were modest run-of-river projects that used only a small fraction of the flow. They caused no perceivable change in upstream or downstream water levels and did not hinder fish migration. The first Beauharnois hydroelectric generating station, built between 1929 and 1932, was of this type and initially diverted only 15% of the river flow towards the Beauharnois Canal. However, to meet the growing demand for electricity, the station was gradually expanded and the intake canal enlarged to the point where 84% of the river flow now passes through the power station (A. Michaud, Planification des équipements, Hydro-Québec, personal communication; see also Fig. 6.6). As more water was diverted, additional structures were built to maintain water levels in the Beauharnois Canal or to create recreational reservoirs.

Figure 6.6 Structures and river flow in the St. Lawrence between Lake St. Francis and Lake St. Louis: the Beauharnois Canal and generating stations

Hydro generating stations were also built near Cornwall–Massena, Niagara Falls, and the St. Marys River at Sault Ste. Marie. The Moses–Saunders hydroelectric generating station, a Canada–U.S. project, was built between 1954 and 1958. It resulted in the disappearance of the rapids at the head of Lake St. Francis and the creation of a reservoir upstream, Lake St. Lawrence. This dam is the main control structure regulating the outflow of Lake Ontario and is operated according to the Lake Ontario regulation plan. At Niagara Falls, water is diverted from the Niagara River above the falls and returned to the river below the falls. The diversion and flow over the falls are regulated by the International Niagara Board of Control of the International Joint Commission (IJC) (Levels Reference Study Board 1993). Two hydro power facilities are located in the Michigan portion of the St. Marys River, and one is located in Ontario. These facilities plus the compensating works are operated according to the Lake Superior regulation plan (Levels Reference Study Board 1993).