Canada is "extremely concerned" about the potential fate of the Line 5 pipeline, emissaries warned Tuesday in advance of a Wisconsin court hearing that threatens to shut down what they call a vital cross-border oil and gas corridor. 

The warning from Canada's embassy in Washington, D.C., comprised Ottawa's first formal comments about the pipeline in months — a lengthy, measured statement that nonetheless made plain its fears for Line 5's future. 

And it leaned hard into three areas always sure to get attention in the U.S.: protecting American jobs and growth, defending continental energy security and honouring treaty obligations to an important and trusted ally. 

"The energy security of both Canada and the United States would be directly impacted by a Line 5 closure," said the statement from the Canadian Embassy in D.C. 

"At a time of heightened concern over energy security and supply, including during the energy transition, maintaining and protecting existing infrastructure should be a top priority."

The economic argument is one the pipeline's proponents have been making for years: a shutdown would cause "significant economic disruption" across the U.S. Midwest, where it provides feedstock to refineries in Michigan, Ohio and Pennsylvania. 

Line 5 also supplies refineries in Ontario and Quebec, and is vital to the production of jet fuel for some of Canada's busiest airports. Some 33,000 U.S. jobs and US$20 billion in economic activity would be imperilled, the embassy warned. 

The source of the alarm is a court dispute in Wisconsin between the pipeline's owner, Alberta-based Enbridge Inc., and the Bad River Band of the Lake Superior Chippewa, through whose territory Line 5 runs. 

Spring flooding has washed away significant portions of the riverbank where Line 5 intersects the Bad River, a meandering, 120-kilometre course that feeds Lake Superior and a complex network of ecologically delicate wetlands.

The band has been in court with Enbridge since 2019 in an effort to compel the pipeline's owner and operator to reroute Line 5 around its traditional territory — something the company has already agreed to do. 

But the flooding has turned a theoretical risk into a very real one, the band argued in an emergency motion last week, and it wants the pipeline closed off immediately to prevent catastrophe.

"There can be little doubt now that the small amount of remaining bank could be eroded and the pipeline undermined and breached in short order," the band's lawyers argued.

"Very little margin for error remains."

Line 5 meets the river on Indigenous territory just past a location the court has come to know as the "meander," where the riverbed snakes back and forth multiple times, separated from itself only by several metres of forest and the pipeline.

At four locations, the river was less than 4.6 metres from the pipeline — just 3.4 metres in one particular spot — and the erosion has continued in recent days at an "alarming" rate, the motion said.

In one case, so-called "monuments" installed to measure the losses show that where there was more than 10 metres of riverbank in early April before the flooding began, only 3.7 metres remained as of last Tuesday.

"Significant erosion is continuing as of the filing of this motion, and the evidence strongly suggests that further bank loss could be substantial and result in exposure and rupture of the pipeline."

Wisconsin district court Judge William Conley is expected to hear oral arguments on the motion Thursday. It's not clear if he'll reserve judgment or rule immediately whether to order Enbridge to shut down the pipeline and purge its contents.

But Conley has already indicated a reluctance to shut down the pipeline, citing the potential economic and foreign-policy consequences, suggesting Tuesday's statement from the embassy was aimed squarely at him. 

"I think Canada is saying, 'Please be aware,'" said Kristen van de Biezenbos, a professor of energy law at the University of Calgary. 

Because there are no alternatives to Line 5 for shipping fossil-fuel energy to Ontario and Quebec, the stakes of a shutdown would likely be higher for Canada than for the U.S., she added. 

"Even knowing that it's not a great idea to be largely dependent on just one source of oil, there hasn't been anything done to change that," van de Biezenbos said. 

"It would be a serious problem for Canada if Line 5 was shut down — not just because of the wider economic impacts for the oilpatch in Alberta, but also because that is the main source of crude oil products for eastern Canada." 

Later Tuesday, lawyers for Enbridge began filing a raft of affidavits and sworn statements from pipeline safety experts, scientists, environmental engineers and even the company's own director of tribal engagement, all in opposition to the request for an injunction. 

One of them, from a Vancouver hydrologist named Hamish Weatherly, acknowledged that the threat of a rupture caused by erosion is higher than it was at the end of last year, but still far from critical. 

"It is thus my opinion based on my knowledge, training and experience that there is not an 'emergency' or 'imminent threat' of a release at the meander," Weatherly's declaration reads. 

A separate declaration from David Stafford, the company's U.S. pipeline compliance manager, said the U.S. Pipeline and Hazardous Materials Safety Administration has been kept apprised of all the latest developments. 

"Since receiving notification of the erosion at the meander, PHMSA has not expressed any concern regarding the safety of Line 5 at this location," Stafford asserts in the document.

Tuesday's filings also included a string of affirmations from senior executives across the Canadian energy sector from companies like Suncor, Cenovus, Imperial Oil, Shell Canada and Superior Gas, among others. 

Canada has already invoked a 1977 pipelines treaty with the U.S. in both Wisconsin and Michigan, where that state's attorney general is also in court trying to get the pipeline shut down. 

Talks under that treaty have been ongoing for months, with the latest session taking place last month in Washington. 

"Canada invoked the treaty's dispute settlement provisions because actions to close Line 5 represent a violation of Canada's rights under the treaty to an uninterrupted flow of hydrocarbons in transit," the embassy said. 

"If a shutdown were ordered because of this specific, temporary flood situation, Canada expects the United States to comply with its obligations under the 1977 Transit Pipelines Treaty, including the expeditious restoration of normal pipeline operations."

The key word there is "temporary," van de Biezenbos said. 

"The pipeline treaty makes it clear that you can order temporary shutdown of international pipelines between the U.S. and Canada for public safety reasons," she said.

"If there is a shutdown that's ordered because of the flooding, then as soon as the flood risk has been abated, then the pipeline has to be brought back online."

This report by The Canadian Press was first published May 16, 2023.