The Shipping Channel

The St. Lawrence shipping channel, also known as the maritime channel, begins downstream of the St. Lambert Lock, which is part of the Great Lakes St. Lawrence Seaway System. This is the main shipping route between the Port of Montreal and the naturally deep water nearly 65 km downstream of Quebec. It covers a total distance of 322 km and is marked with large red and green buoys. It contains no locks and is open year-round.

The shallow water of Lake Saint-Pierre was noted as far back as 1535. During his second voyage, the explorer Jacques Cartier attempted to travel upstream in his smallest ship, the Émérillon. After the ship ran aground on a shoal in Lake Saint-Pierre, Jacques Cartier and his crew had to use smaller boats to cross the lake and reach Hochelaga.

Upstream of Quebec City, the river presented a number of obstacles, most notably Lake Saint-Pierre. For a long time, large ships therefore could not go past the Port of Quebec City. To bring cargo further west, it had to be transferred to smaller vessels. This increased the cost of shipping, since lighterage and towing fees had to be paid. As of the early 19th century, merchants in Montreal began pressuring Public Works Canada to carry out dredging operations that would allow safe passage of ships up to the Port of Montreal. Work on dredging a channel through Lake Saint-Pierre finally started in 1844.

A straight channel was plotted through Lake Saint-Pierre, diverging from the curved path of the existing natural channel. Between 1844 and 1847, a channel 11 km long, 30 m wide and 2.1 m deep was dredged out. In 1850, the Montreal Harbour Commissioners took over dredging operations and changed the route back to follow the natural channel. Work started again the following year and continued until 1854. During this period, the main focus was on removing shoals in Lake Saint-Pierre. The main shoal, in the middle of the lake, lay under just 3.3 m of water and covered a distance of 7 km. In this period, ships would take the Grand Chenal between Île de Grâce and Île Ronde.

Learn more about how humans have transformed Lake Saint-Pierre over the past 150 years

Between 1855 and 1865, the channel was dredged to a depth of 6.1 m over a distance of 16.3 km. Work began again in 1875 and ended in 1882. At that time, the channel was extended to a length of 28.1 km and cut deeper to 7.6 m. The straight parts of the channel were 91 m wide, while on the curves it expanded to a width of 131 m. Between 1883 and 1888, the channel was further dredged to a depth of 8.4 m. In the early 20th century, Public Works Canada again dredged the channel to a depth of 9.1 m. Its maximum width in the curved portions reached 243 m.

Between 1910 and 1917, dredging operations dug the channel down to 10.7 m. There were no further new dredging operations, only maintenance dredging to remove sediment build-up in certain sections of the channel. From 1929 to 1934, water levels in the St. Lawrence were extremely low. To maintain a depth of 10.7 m in the channel, an additional 0.3 m had to be dredged.

Between 1937 and 1952, the channel through Lake Saint-Pierre was enlarged to a width of 167 m, then enlarged again to 244 m between 1968 and 1970. In 1992, the section between Montreal and Deschaillons was dug down to 11 m, and the channel outside Lake Saint-Pierre was widened to 230 m. The channel was dredged again in 1998 to ensure a depth of 11.3 m between Montréal and Deschaillons. A total of 200,000 m³ of sediment was removed, 116,700 of which came from Lake Saint-Pierre. Since 1998, only maintenance dredging has been carried out in the shipping channel.

Previously, dredged sediments were deposited on either side of the channel. During the 20th century, they were instead placed in a single spot, creating Île aux Sternes at the outflow of Lake Saint-Pierre. This island was designated as the Marcel-Léger ecological reserve in 1981 to highlight its rich flora and fauna.

In the 1930s, five weirs were built between islands in the Lake Saint-Pierre Archipelago. These structures blocked certain channels; they were intended to raise water levels up to the Port of Montreal and increase water flow in the shipping channel. The weirs had to be repaired several times because of erosion caused by strong currents and moving ice.

The weir between Île de Grâce and Île Ronde blocked the entrance to the Grand Chenal, formerly used by ships. All shipping now had to pass through the channel between Île des Barques and Île à la Pierre. To make this narrow, dangerous passage wider and straighter, Transport Canada purchased Île des Barques and cut a straight line into it along the shipping channel.

The construction of the shipping channel, beginning in 1844, gradually increased the number of ocean-going ships arriving at the Port of Montreal. In 1854, six steamships and 252 sailing ships arrived at the port. In 1882, some 40 years into the project, the port welcomed 352 steamships and 296 sailing ships. Today, the busy Port of Montreal is the largest port in Quebec. It accommodates a wide variety of cargo ships, cruise ships and enormous container ships. The Port of Montreal is considered the leading container port serving the North Atlantic market.