A snapshot of vessel movements on the Great Lakes St Lawrence Seaway. Source: MarineTraffic Density Maps 2020

The Great Lakes St Lawrence Seaway is a 3,700 km artery from America and Canada’s interiors to the North Atlantic Ocean. The bilateral waterway, which consists of lakes, locks, canals and channels, starts at Duluth in the US state of Minnesota on the western side of Lake Superior and extends to the Atlantic Ocean in the east.

It is the longest inland deep-draft navigable seaway in the world and is often dubbed and marketed as Highway H2O. According to the Chamber of Marine Commerce, it connects “more than 110 commercial ports in Canada and the United States”. 

With an average sailing time of 8.5 days, the waterway takes in some of North America’s largest ports including Duluth-Superior and Detroit in the US and Montreal in Canada.

According to the Great Lakes St. Lawrence Seaway Development Corporation, nearly 25% of vessel traffic travels outside of the waterway to ports overseas, reaching markets in Europe, the Middle East and Africa and beyond.

Considered one of the world’s most impressive waterways, the route as it stands today was realised in 1959, which saw the completion of eight locks across six canals on the St Lawrence River between Lake Ontario and Montreal. This intricate and complex lock system lifts vessels 75 m as they sail between Montreal and Lake Ontario.

However, the deep-draft navigable waterway would not have been possible without the completion in 1829 of the 24-km Welland Canal – of a series of eight locks that link Lake Ontario and Lake Erie. Upgrades have been made on both canals in the intervening years.

Vessels of the maximum size that can transit the waterway have their own term. Known as Seawaymaxes, these vessels can be no more than 225.5 m in length, 23.77 m wide, have a draft of no more than 8.08 m, and be no more than 35.5 m tall.

These vessels directly serve markets in the Canadian provinces of Ontario and Quebec, and US states of Illinois, Michigan, Ohio, Indiana, Wisconsin, Minnesota, New York, and Pennsylvania. Cargo of all types continue to be moved between regions and to international markets via the waterway, with certain commodities dominating trade. According to the Great Lakes St. Lawrence Seaway Development Corporation, “Annual commerce on the system exceeds 200 million net tons (180 million metric tons), and there is still ample room for growth”.

The manufacture of steel has always been an important part of the US economy and in 2019 it was ranked the fourth largest steel producer in the world. According to the American Iron and Steel Institute for the week ending 28 August this year, the Great Lakes district was the second-biggest producer of steel representing 34 %, with 638,000 net tons. It was second only to the Southern district which produced 811,000 net tons of steel.

It follows that a significant volume of this steel will find its way to the Great Lakes St. Lawrence Seaway. It also follows that wherever there is steel production there must be iron ore, with iron ore carriers a regular fixture on the waterway. Other significant cargoes, according to the Development Corporation, include coal, again for steel production and also power generation, limestone which also serves steel production and is also used in construction, and general cargo, including steel products.

Agricultural products are also a major commodity found on the waterway, and according to Canada’s St. Lawrence Seaway Management Corporation they “represent about 40% of all seaway trade”. These cargoes from both Canada and the US are destined for international markets and include wheat, corn, soybeans, barley, oats, and flaxseed.

Related: Shipping trends at a glance

The volume of steel and agriculture combined mean bulk carriers are a regular sight on the waterway. According to MarineTraffic data, a total of 525 vessels of 4999-dwt or more were recorded on the waterway from June to August this year, and 174 were bulk carriers, with a further 18 self-discharging bulk carriers.

The second most popular with 75 vessels was oil and chemical tankers. According to the Canadian government “tankers carrying oil products account for 7% of all shipments completed” in the waterway, although none of this is heavy fuel oil.  

Vessels that moved within the Great Lakes St Lawrence Seaway from 1 June to 31 August this year. Source: MarineTraffic

Despite the importance of the waterway, its location dictates that its fresh water freezes over and so must close during the heavy winter months. Its closure changes depending on the weather in each given year, although the American Great Lakes Ports Association says “the system’s locks have opened as early as March 20 and as late as March 31. The closing date has ranged from December 24 to December 31”.

Vessels can still get access as far as Montreal due to icebreakers, but going west and the Welland Canal is drained for the winter months.

The association is campaigning for the extended opening of the waterway, and is in favour of harmonising the “seaway’s opening and closing dates with those of the Soo Locks in northern Michigan [which link Lake Superior and Lake Huron]. Doing so would establish a fixed navigation season for the entire Great Lakes navigation system from March 25th – January 15th,” it says.

Related: The big thaw

However, with global warming making a year-round route through the Arctic increasingly likely, the Great Lakes St Lawrence Seaway may find that it too can offer a navigable waterway through all four seasons.