The Saint Lawrence Seaway is a system of locks, canals and dredged channels that lets ocean-going ships sail from the Atlantic Ocean into the Great Lakes of North America. Strictly speaking, the Seaway runs about 600 km from Montreal to Lake Erie. Along the way, 15 locks, seven on the St. Lawrence River and eight on the Welland Canal, lift ships about 168 m, roughly the height of a 50-storey building. Built jointly by Canada and the United States, it opened to shipping in April 1959, and with the connecting channels of the upper lakes it forms a navigable route of about 3,700 km from the Gulf of St. Lawrence to Duluth, Minnesota, deep in the heart of the continent.
Why a Seaway Was Needed
The St. Lawrence River drains the Great Lakes to the Atlantic, but for most of history ships could not follow it inland. Just upstream of Montreal, the Lachine Rapids blocked the way, and further up, between Montreal and Lake Ontario, the river dropped through a series of rapids such as the Long Sault. Between Lake Ontario and Lake Erie stood the greatest obstacle of all, Niagara Falls and its gorge, where the land falls about 100 m.
Canals had been cut around these obstacles since the nineteenth century. The Lachine Canal opened in 1825 and the first Welland Canal in 1829. But by the early twentieth century their locks were too small for anything but specially built small ships, only about 4.3 m deep. Proposals for a deep seaway were debated for decades, and a treaty was signed in 1932, but the United States Senate rejected it in 1934, largely because railway companies and East Coast ports feared the competition. In 1951 Canada decided to build a seaway on its own if necessary. Faced with that, Congress approved American participation in 1954 through the Wiley-Dondero Act, and construction began that year.
Building It, 1954 to 1959
The project was one of the largest engineering works of its time. Crews excavated and dredged tens of millions of cubic metres of earth and rock, built locks, dams and bridges, and rerouted railways and highways. It was built together with a hydroelectric project on the international stretch of the river, whose Moses-Saunders Power Dam, between Massena, New York, and Cornwall, Ontario, still generates electricity for both countries. Ontario Hydro and the Power Authority of the State of New York paid for the power works, and the two national seaway authorities paid for the navigation works.
Ships began using the Seaway on 25 April 1959, when the Canadian icebreaker d'Iberville led the first vessels through. The official opening came on 26 June 1959, when Queen Elizabeth II and President Dwight D. Eisenhower sailed together on the royal yacht Britannia to the ceremony at St. Lambert, near Montreal.
The Lost Villages
The hydro dam needed a large reservoir, and its creation drowned a stretch of the Ontario shore. On 1 July 1958, a date remembered locally as Inundation Day, a temporary cofferdam was blasted and the water began to rise over a series of riverside communities, including Aultsville, Farran's Point, Dickinson's Landing, Wales, Moulinette and Mille Roches. About 6,500 people had to move. Some houses were lifted onto giant trucks and moved to two new towns, Ingleside and Long Sault. Others were demolished, and churches, cemeteries and roads lie beneath what is now Lake St. Lawrence. At low water, sidewalks and foundations can sometimes still be seen. A few surviving buildings were moved to Upper Canada Village, a heritage park near Morrisburg.
The Mohawk communities of Kahnawake, near Montreal, and Akwesasne, on the border near Cornwall, also lost land and access to the river, and they have long argued that the project was pushed through without their consent.
Travelling Upstream, Lock by Lock
A ship heading inland from the Atlantic first sails about 1,000 km up the Gulf of St. Lawrence and the river to the port of Montreal, where the Seaway begins. It enters the South Shore Canal, bypassing the Lachine Rapids, and climbs through the St. Lambert and Côte Ste. Catherine locks. Next it crosses Lac Saint-Louis and enters the Beauharnois Canal, where two locks lift it past a large hydroelectric station. After Lake Saint Francis it reaches the international section, where two American locks, the Snell and Eisenhower locks at Massena, New York, carry it past the Moses-Saunders Dam. The Iroquois Lock, the last of the seven on the river, controls the water level of Lake Ontario, lifting ships only a few feet. Then the ship passes through the Thousand Islands, a scenic maze of more than 1,800 islands, and into Lake Ontario, about 75 m above sea level.
To go further, it must cross the Niagara Peninsula through the Welland Canal, about 43 km long, from Port Weller on Lake Ontario to Port Colborne on Lake Erie. Its eight locks lift ships about 100 m. Locks 4, 5 and 6 are twin flight locks, where ships climb a steep slope in steps, one lock opening straight into the next, and ships going up and down can use them at the same time. Our guide to the Welland Canal describes its four versions since 1829. Once on Lake Erie, ships can continue to Detroit, Chicago, Duluth and the rest of the Great Lakes, passing the Soo Locks at Sault Ste. Marie to reach Lake Superior.
Every lock works on the same simple principle, using no pumps at all. A ship heading upstream sails into the chamber and the gates close behind it. Valves open and water from the higher level flows in by gravity through culverts in the lock walls, raising the ship, typically by around 10 to 15 m, in about seven to ten minutes. When the water matches the level ahead, the upper gates open and the ship sails out. Going downstream, the process runs in reverse, draining the chamber to the lower level. A ship usually needs about a day to climb from Montreal to Lake Ontario and around half a day to cross the Welland Canal, while the whole voyage from the open Atlantic to Duluth takes roughly eight or nine days.
The locks on the Seaway are all built to the same size: about 233.5 m long, 24.4 m wide and 9.1 m deep over the sills. The largest ship that fits, called a Seawaymax vessel, is about 225.5 m long and 23.8 m wide and can carry around 28,000 tonnes of cargo. Some of the world's largest bulk carriers, tankers and container ships are far too big, which has always limited the Seaway's role in world trade.
What Moves on the Seaway
The Seaway carries bulk cargo more than anything else. Grain from the Canadian Prairies and the American Midwest moves downstream from ports such as Thunder Bay and Duluth to be exported, and iron ore from Quebec and Labrador moves upstream to steel mills in Ontario and the United States. Other major cargoes include coal, salt, cement, gypsum, steel and liquid bulk such as fuel. In a typical year, it handles around 35 to 40 million tonnes of cargo. Traffic peaked in the late 1970s, when it carried more than 70 million tonnes, then declined as the steel industry of the Great Lakes shrank and container shipping grew.
Two kinds of ship use the route. Lakers are long, narrow bulk carriers built for the lakes, and many of them stay in the lakes and the Seaway all their lives. The very largest lakers, over 300 m long, are too big for the Welland Canal and never leave the upper lakes. Salties are ocean-going ships that sail in from overseas.
The Winter Shutdown
Unlike most shipping routes, the Seaway closes every year. Ice forms on the river and in the canals, and the locks need maintenance, so the Seaway usually closes in late December and reopens in late March, a gap of about three months. The last ships of the season race to leave before the closing date, and any vessel still inside may be trapped until spring. The Canadian and American operators, the St. Lawrence Seaway Management Corporation and the Great Lakes St. Lawrence Seaway Development Corporation, use the winter to repair locks and gates.
The Price Paid by the Lakes
The Seaway also opened the Great Lakes to living invaders. Ocean ships take on ballast water in foreign ports and discharge it when they load cargo. In the decades after 1959, that water released species such as the zebra mussel, which arrived from the Black Sea region in the late 1980s, and the quagga mussel and round goby. Zebra mussels spread across the lakes, clogged water intake pipes and changed the lakes' ecology, costing billions of dollars. Since 2008, ships entering the Seaway from outside North America have had to flush their ballast tanks with salt water at sea, and the rate of new invasions has fallen sharply. The lakes themselves are described in our guide to the Great Lakes.
Today the Seaway is still a working waterway, busy with lakers and salties from spring to Christmas, and a small but growing cruise trade brings passengers through the Thousand Islands and the locks each summer. It ends where it began, on the great river that drains the lakes, whose whole course is covered in our guide to the St. Lawrence River.