The Nova Scotia government argued in court on Tuesday that Ottawa is solely responsible for infrastructure that protects the low-lying strip of land that links the province with New Brunswick.

Nova Scotia says the federal government should pay the entire cost of upgrading the centuries-old dikes that protect the Chignecto Isthmus from flooding, a project expected to cost $650 million, The Canadian Press reported.

Ottawa has agreed to pay only half the bill. It argues the dikes have long been used to protect farmland, which means they are covered by a section of the Constitution that says agriculture is a responsibility shared by the two levels of government.

A provincial government lawyer, however, told Nova Scotia’s Court of Appeal on Tuesday that the extensive network of dikes protect much more than just farmland. Daniel Boyle said the land bridge now includes a Canadian National Railway line, the Trans-Canada Highway, buried fibre optic cables and overhead electricity lines.

Boyle told the three-justice panel the dikes protect interprovincial trade and communications links, which fall under exclusive federal jurisdiction. He said the federal government has an obligation to protect those links, which are increasingly threatened by flooding caused by fierce and frequent storms and rising sea levels.

Boyle, who represents Nova Scotia’s attorney general, also noted that a three-kilometre stretch of the railway line is part of the extensive network of dikes, which were built by Acadian farmers in the 1600s. There are now about 35 kilometres of dikes that help protect roads, railways, farms and communities.

“A flood could sever Nova Scotia from the rest of Canada,” he said.

Michael Wood, chief justice of Nova Scotia, pointed out that agriculture hasn’t disappeared from the area, which he said raised questions about shared jurisdiction. But Boyle said the dikes have “much broader importance,” stressing that the province can’t act on its own to protect what has evolved to become an essential “trade corridor” that is facing serious risks.

The lawyer said an eight-metre storm surge would flow over the dikes and submerge the highway and the rail line. At 12 metres, “Nova Scotia would effectively become an island,” he said. “It’s a real concern.”

That level of catastrophic flooding would effectively cut off $50-million worth of trade every day, he said, adding that the Port of Halifax would be unable to use trains or trucks to ship goods to the rest of Canada.

“Provinces don’t have jurisdiction over the railway,” Boyle said, adding that one of the main reasons Nova Scotia joined Confederation in 1867 was a promise that a new national government would build a railway to link the province’s economy with other rapidly growing provinces.

“It wasn’t just one piece of infrastructure,” he said. “It was the wider promise of what that infrastructure brought.”

At one point, Justice David Farrar asked Nova Scotia lawyer Jeremy Smith to explain why the court was asked to settle what is essentially a political dispute over jurisdiction. Smith said the court’s decision would “provide guidance and some certainty to both levels of government.”

During a hearing in March, federal lawyer Lori Ward said rail lines can be raised and transmission lines can be buried, suggesting the dikes are not essential for their protection.

She also questioned whether enough was known about “which dike protects what” on the isthmus, though Boyle argued Tuesday that the dikes represent a large network that is only as strong as its weakest part. Ward characterized Nova Scotia’s case as an attempt to “enlist the court” to aid in what is really a funding dispute, saying the panel should decline to answer the province’s question as to what level of government is responsible for protecting infrastructure. The three justices plan to deal with that issue at a later date.

New Brunswick and P.E.I. are supporting Nova Scotia’s case. The hearing resumes Wednesday.

This report by The Canadian Press was first published May 20, 2025.