American border agents are increasingly concerned about the northern boundary with Canada, saying the number of people entering the U.S. through back roads, forests and even across rivers is surging.

"We've seen an increase coming into the United States from Canada," U.S. Border Patrol Houlton Division chief Dennis Harmon says.

He is responsible for the north-eastern frontier, through the Maine-New Brunswick line and the shared waters along the Atlantic.

At least 32,000 asylum seekers have crossed from the U.S. into Canada in recent months, and that influx continues. But the leading edge of those claimants, say authorities with U.S. Customs and Border Protection, are likely to soon face deportation from Canada — so now some of them are heading back south.

"The [Canadian] government has deemed that their claim is not valid and is in proceedings to remove them from the country," Harmon says. "We then have some of those people trying to effect their illegal entry into the U.S."

'We want to stop the illegal entry before it even happens. So if we have a non-immigrant who is trying to cross here, we’ll do what we can to deter that activity,' the U.S. Border Patrol's Houlton Division Chief Dennis Harmon says. (Jean-Francois Bisson/CBC)

Along this one sector of the border, apprehensions of people crossing illegally are up 60 per cent over the past year, although the numbers remain minuscule relative to activity on the border with Mexico.

Along the sparsely populated and relatively remote New Brunswick-Maine border, patrol agents have apprehended 54 people so far this year, compared to 33 in all of 2017. That trend has been seen across much of frontier's full length, according to U.S. Border Patrol figures.

Still, American authorities say their own projections and intelligence work suggest a reason to be on guard. In anticipation of more people trying to cross from Canada into the U.S., they have already increased their staffing levels and added detection technology along the Canadian border.

Two gravel roads near Hodgdon, Maine, parallel the border - on the left is Canada, on the right is the U.S., where American border officers monitor for illegal jumpers. (David Common/CBC)

U.S. agents are also using jetboats to conduct high-speed surveillance along the rivers that act as the separating line between the two neighbouring nations.

While it may seem strange that someone would attempt to cross a river surrounded by dense forests rather than simply walking across shared roads, it does happen.

In 2014, for example, agents arrested John Calvin [an adopted name] when he swam across a river to enter the U.S. after his refugee claim was denied in Canada. The 24-year-old's family is connected to Hamas and the Muslim Brotherhood, though it appeared the gay man, who had converted to Christianity, was trying to escape the family legacy when he was caught. He has since legally settled in the United States.

Who's crossing

Division chief Harmon says more people are following in Calvin's footsteps and using Canada as a gateway to the United States, in part because of the differences between Canadian and American visa requirements. It's much easier for people from some nations to visit Canada legally than the U.S.

Mexican citizens, for instance, can enter Canada without first applying for a full visa.

Where rivers separate New Brunswick from Maine, U.S. Border Patrol officers scan the shoreline from boats for people and fresh footprints. The officers have apprehended people trying to wade or swim across these shallow waters. (Jean-Francois Bisson/CBC)

"Sometimes it's just easier for them to fly into Canada without a visa and then cross into the U.S., than to use a smuggling route out of Mexico," says Harmon, adding "it's cheaper to get that airline ticket and just come across."

A low-cost airfare from Mexico City to a Canadian destination costs around $400, while a smuggling operation across the Mexico-U.S. border will often charge five times that amount.

The preference and protocol for U.S. agents is to stop potential border crossers before they make it over the dividing line between the countries — and can then make a claim for status.

Officials with U.S. Customs and Border Protection stress a good and speedy working relationship with the RCMP helps with deterrence. While Mounties cannot arrest someone for simply being near the border, they can watch and question an individual's intent.

The U.S. Border Patrol works with the RCMP to monitor both sides of the U.S./Canada border. They follow up on suspicious activity, trying to stop people before they can cross illegally. (Jean-Francois Bisson/CBC)

The law says those who have entered either country must declare the purpose of their visit. If it appears their presence near the border doesn't match their stated purpose, officials may take action to have the visa cancelled (if the person has one) or to have them removed from the country.

But while it attracts illegal crossers, that doesn't mean the Canadian route is easy — without on-the-ground connections, just getting to the border from the Canadian side can be a challenge. Taxis are expensive, and travellers with no clear destination prompt phone calls to authorities from suspicious residents on both sides of the border.

However, once a person successfully makes it across at a point other than a legal crossing, it can be easy to move south. Maine is the starting point of the I-95 interstate corridor, a few hours drive from Boston and then, soon after, New York City.

Watch David Common's feature from The National about the U.S. Border Patrol: