GRAND MANAN, N.B. -- A little-known cross-border dispute that has simmered between Canada and the United States since the late 1700s is now approaching the boiling point.

In the past two weeks, at least 10 Canadian fishing boats from New Brunswick have been intercepted by U.S. Border Patrol agents while fishing in the disputed waters around Machias Seal Island, a spokesman for the fishermen says.

Laurence Cook, chairman of the advisory board for Lobster Fishing Area 38, said Wednesday that some Canadian vessels were boarded by American agents who asked about possible illegal immigrants.

"There's been a bit of a misunderstanding there somewhere," Cook said in an interview. "They're in international waters, so border patrol shouldn't be boarding Canadian vessels."

Machias Seal Island, which is about 19 kilometres southwest of Grand Manan Island and east of Maine, is in a disputed area known as the Grey Zone, where lobster fishermen from both Canada and the United States have long fished side by side.

The small island is a flat, treeless piece of rock, which includes a large colony of puffins and a lighthouse that is manned by two Canadian lightkeepers year-round.

However, both Canada and the United States claim sovereign jurisdiction over the island and the surrounding waters at the mouth of the Bay of Fundy.

As lucrative lobster catches have increased in the zone, competition between fishermen has intensified in the past decade.

"Neither country accepts that there is a Grey Zone," said Stephen Kelly, a research scholar at Duke University in Durham, N.C., and a former American diplomat who served in Canada. "That's created more tension in the area over the last decade."

Kelly said both countries have done very little to assert their claims.

"Sometimes doing nothing is better," he said. "But in this case, just because it looks like it's not broken can be very deceiving -- especially with our new president in the United States. The last thing Canada wants is for Donald Trump to seize on this as an example of U.S. sovereignty being challenged."

The suggestion that the border agents were looking for illegal immigrants seems improbable, he said.

"That's possible, but ... the Gulf of Maine is not a major route for illegal immigrants sneaking into the United States," Kelly said. "If anything, people are sneaking the other way. They're trying to get out of the U.S. and into Canada to claim asylum."

He said drug smuggling is a more relevant concern.

On Grand Manan, local residents are speaking out about the U.S. intervention, said Cook.

"I guess the comment on the street would be: 'Typical American bullies,"' he said. "They're not happy about it, and they don't think (the Americans) have any business doing this."

Cook said he's never before seen border patrol agents in the area, where the U.S. Coast Guard typically patrols. He said he had no idea why American authorities are suddenly flexing their muscles.

"All of a sudden the attitude has changed. What caused that? You'll have to talk to border patrol."

The U.S. Border Patrol, which is part of U.S. Customs and Border Protection, declined to comment and referred all inquiries to the U.S. State Department, which did not respond to a request for an interview.

Global Affairs Canada distributed a brief statement saying it is investigating "these incidents that occurred in Canadian waters."

Spokesman John Babcock said the Canadian government is also talking with U.S. agencies, though he did not provide details about the fishermen's allegations or Ottawa's response.

"Canada's sovereignty over the Machias Seal Island and the surrounding waters is long-standing and has a strong foundation in international law," Babcock said.

"Until the matter of the boundary is resolved, we will continue to take practical steps with the U.S. to ensure that the area is well-managed. Canada and the U.S. have a long history of co-operation which ensures that fishing in this area is well-managed and safe for both countries."

The Grand Manan Fishermen's Association issued a statement that used much the same language. As well, the group suggested the actions of the U.S. agents may have been routine.

"We understand that a few Grand Manan fishermen were approached by the United State Border Services during the month of June. Our understanding is that this was a part of a regular exercise being conducted along the U.S. marine border."

The association said it has enjoyed a respectful and cordial relationship with its U.S. counterparts.