As Ni­ger­ian asylum seekers flood into Canada across a ditch in Upstate New York, Canadian authorities are asking the United States for help — but not with managing the influx at the border.

Instead, they want U.S. immigration officials to reduce the foot traffic by screening Nigerians more stringently before granting them U.S. visas.

It is a ripple effect that few expected last summer when people, mostly Haitians, began to walk into Quebec via an “irregular” border crossing north of Plattsburgh, N.Y., and seek refugee status.

With the coming of spring, the flow has picked up again. But recently, the asylum seekers have been mostly Ni­ger­ian, and their route to the border is more problematic, Canadian officials say.

Many Haitians had lived in the United States for years before suddenly learning they would lose their protected status and fleeing north. But many of the Nigerian asylum seekers are arriving in Quebec with recently issued U.S. visitor visas, said Mathieu Genest, a spokesman for Canada’s immigration minister.

“They’re not using the visa for the reason it was intended for,” he said.

Canada is not asking U.S. officials to refuse entry to Nigerians, Genest said. It is seeking stricter screening to ensure that Nigerians who are granted U.S. visitor visas truly intend to return home.

The request is an unsurprising one between two countries that have collaborated for decades on migration-related matters. But it also is a sign that Canada is feeling new pressure on its borders as U.S. immigration and refugee policies shift.

“Instead of Trump throwing us back to Nigeria, we appreciate Canada right now for accepting people,” said one Nigerian man who walked into Quebec in March.

The man, who gave his name only as Isaac, carried a single duffel bag as he prepared last week to move with his family into an apartment in Montreal. Many Nigerian claimants in Montreal will not speak to reporters for fear of jeopardizing their status.

For six weeks, Isaac and his family have stayed at a shelter on the city’s outskirts, a onetime youth detention center that was converted last year into emergency housing for refugee claimants.

“I don’t want to go back to Nigeria,” he said. “Nobody’s safe.”

He arrived in Texas early last year on a visitor visa, he said, with plans to get another kind of visa when it expired or else claim U.S. refu­gee status for himself, his wife and their two young children.

But the election of Donald Trump changed his mind. “He doesn’t want immigrants,” he said. “Canada is open for an immigrant.”

The Canadian government has been trying to tone down its welcoming image — or, rather, to provide accurate information about how it processes refugee claims. Ethnic communities in the United States have been warned that actually winning refu­gee status here is hard.

But the campaign has been ineffective. As of mid-April, nearly 6,000 people had entered Quebec unofficially, three times as many as during the same period in 2017. And in 2017, claims across the country had doubled from the year before.