Vessel traffic at the Port of Duluth-Superior, the Great Lakes' largest port by tonnage, fell 23% year on year through August, as the trade dispute between the United States and Canada intensified and put pressure on one of the countries' key shipping corridors.
Calls by U.S.-flagged vessels fell about 19%, while calls by incoming Canadian vessels dropped 37%, amid pressure on coal and iron ore trade and growing uncertainty over U.S. tariffs.
A trade corridor supporting $6 trillion in economic activity
The Great Lakes and the St. Lawrence Seaway form a major trade artery between the United States and Canada. The route stretches for about 2,300 miles, or nearly 3,700 kilometers, linking the heart of North America with the Atlantic Ocean.
About 200 million tonnes of goods move through the lakes and the seaway each year, including coal, grain, iron ore, limestone, salt, sand and stone. Economic activity in the region and the surrounding states and provinces is estimated at about $6 trillion, underscoring the integration of supply chains on both sides of the border over decades.
Kevin Beardsley, executive director of the Duluth Seaway Port Authority, said a prolonged dispute increased the risk that Canada would develop different supply chains. He said he hoped an agreement could be reached that would allow normal commercial activity to resume.
Coal and iron ore shipments decline
Coal volumes handled through Duluth-Superior totaled about 4.7 million tonnes in 2025, but are on track to reach only about 500,000 tonnes this year, the lowest level since 1973. Most of the decline is due to the closure of a coal plant, along with a drop in northbound iron ore shipments.
Domestic iron ore shipments from Duluth-Superior are running about 40% below the pace of 2025, as U.S. tariffs on metals have hurt Canada's steel industry. Iron ore volumes through the port fell by about 3 million tonnes last year from the previous year, with most of the decline attributed to weaker exports to Canada.
Canada explores alternative routes
Trade tensions have prompted Canadian authorities to examine options for reducing their reliance on the U.S. market. The Hamilton-Oshawa Port Authority and the city of Sault Ste. Marie in Ontario are working on a proposal to build a new port and develop road and rail networks to connect Canada's resource-rich regions with domestic markets and overseas trading partners.
The authority's chief executive, Ian Hamilton, said reducing trade between the two countries might be possible, but warned that disrupting existing supply chains would raise costs on both sides of the border.
The United States and Canada share management of the Great Lakes and St. Lawrence system. Canada operates 13 locks, compared with two operated by the United States.
Disputes over competition and fleet renewal
The disputes extend to competition rules in the shipping industry, with U.S. companies saying they face unfair Canadian practices. The Lake Carriers' Association says these rules have contributed to the shrinking of the U.S. fleet and given Canadian companies a larger presence in two-way trade across the lakes. It also criticizes some Canadian operators' reliance on vessels built in China.
Canadian shipping industry representatives, however, say the purchase of vessels from China reflects the limited number of shipyards capable of building lake carriers with specialized designs, rather than a preference among Canadian companies for Chinese manufacturers.
Older U.S. carriers are facing pressure from declining coal and weak iron ore trade, while ports are seeking to rely more on higher-value cargoes such as equipment for oil and gas projects and wind power. Port officials say stable trade between the United States and Canada is essential to the sector's future, given the interconnected transport and supply networks between the two countries.
