Editor's note: This story was updated Nov. 27 to include a better understanding of impacts to ore shipments.

Industry leaders joined congressional counterparts Monday in opposing a remedy to relieve flooding Lake Ontario by opening higher outflows at the Moses-Saunders dam on the nearby St. Lawrence River.

Last week, the International Joint Commission in charge of water regulation approved a plan to open the floodgates in order to lower lake levels on the easternmost of the Great Lakes.

Closing the St. Lawrence Seaway in December to accommodate higher water outflow at the Moses-Saunders dam could cost the Canadian and U.S. economies $193 million per week, the Chamber of Marine Commerce said Monday. This would impact farmers’ grain exports and manufacturing plant operations and disrupt deliveries of fuel, construction materials and road salt for winter to cities throughout the region.

Taconite iron ore shipments would be considerably less impacted since ore boats traverse mainly through the four other lakes. While the overwhelming majority of Minnesota’s iron ore is shipped to the destinations on the lower Great Lakes, there is a portion (less than 8 percent in 2018) that is exported beyond Lake Ontario and/or transshipped through the seaway to points abroad, according to the Duluth Seaway Port Authority.

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“As residents ourselves of Great Lakes communities affected by flooding and storm damage, we share in the concern regarding record-high water levels," Deborah DeLuca, Duluth Seaway Port Authority executive director, said in a news release. "However, the minor water level relief that would result from increased December outflow through the Moses-Saunders Dam would be negligible at best. Concurrently, increasing the outflow to levels unsafe for navigation would do immeasurable and long-term harm to producers and consumers throughout the entire Great Lakes region and the United States as a whole.

"We’re all eager for solutions, but opening the flow on a single dam in December isn’t a meaningful solution, especially when weighed against the associated adverse effects.”

The Chamber of Marine Commerce said a negligible 4-centimeter-per-week reduction would result from the plan — coming at a huge cost to commercial navigation.

“We have the greatest sympathy for Lake Ontario and St. Lawrence River residents and business owners that have been impacted by flooding due to unprecedented weather conditions. This situation has also cost our supply chain millions of dollars,” Chamber of Marine Commerce President Bruce Burrows said. “Halting St. Lawrence Seaway shipping altogether would cause major harm to our economy and achieve no noticeable benefit for flooding victims."

Burrows called on the International Joint Commission and government leaders to collaborate with affected stakeholders to find solutions that look at shoreline resiliency, flood management zones and what can be done during the winter when the St. Lawrence Seaway is closed for eight weeks to navigation starting Jan. 15.

"The costs of stopping commercial navigation at this critical point in December will significantly affect industries that have organized their supply chains around the Seaway’s shipping season," the Chamber said. "Even if companies were able to find alternative transportation (with this very short notice), this would cost considerably more and force huge volumes of cargo onto thousands of trucks at the detriment to the environment and road congestion."

In a Nov. 20 letter, 20 members of Congress from the Great Lakes region, including Rep. Pete Stauber, R-Hermantown, urged the International Joint Commission to ensure the seaway remains open during the navigation season.

"The Great Lakes, including communities in our districts are facing high-water levels. We understand that this problem is real. However, we urge the commission to reject a short-term solution for Lake Ontario that risks commerce in the region by causing the Saint Lawrence Seaway to close during the navigation season," they wrote. "Any closure of the Seaway during the navigation season will impede maritime commerce and negatively impact international trade to and from our states."

The International Joint Commission did not respond to a News Tribune request for comment Monday.

In June, the Chamber of Marine Commerce and Duluth Seaway Port Authority opposed a similar plan by the International Joint Commission to open the Moses-Saunders Dam wider to alleviate Lake Ontario's high water levels.

The groups warned it could cost the shipping industry upward of $1 billion in financial damage to the U.S. and Canadian economies. Ultimately, the commission maintained outflow levels through the dam that still allowed for safe shipping.