MASSENA, N.Y. - U.S. Border Patrol agent Glenn Pickering slowed his rumbling snowmobile to a stop and eyed two trails of churned-up snow running down a riverbank.
They were snowmobile tracks leading out onto the frozen St. Lawrence River between New York and Canada. At night smugglers race across the ice with bags of marijuana. Pickering shielded his eyes with his hand as the wind covered the tracks; he couldn't see whether they went across the border.
"There are all these islands out here, and the snowmobiles just come shooting across," he said. "It's a constant battle."
This is the United States' forgotten border, where federal agents and police play cat-and-mouse with smugglers and illegal immigrants along 4,000 miles of a mostly unmarked and unfortified frontier.
Unlike the border with Mexico, where drug-related violence has exploded, the northern border rarely makes headlines.
That changed this month after a U.S. Government Accountability Office report warned that the terrorist threat from Canada was higher than that from Mexico because of the vast swaths of unprotected frontier.
Just 32 miles of the border have an acceptable level of Border Patrol security, with agents available to make on-site arrests, the report said.
Senators from northern border states urged the federal government to deploy military radar and more unmanned planes. The head of the Senate's Homeland Security committee, Joe Lieberman (I-Conn.), suggested the U.S. should consider requiring Canadians to obtain visas.
"Our country is so focused on the southern border," said Republican Rep. Candice Miller of Michigan, who will chair a hearing about the report today. "At the same time the northern border is essentially wide open."
Drug seizures and crime along the Canadian border are nothing compared with the southern border activity, said Mark Salter, an expert on national security at the University of Ottawa.
Canada's stronger economy and smaller population - about 33 million, compared with 147 million in Mexico and Central America - also means there is less illegal immigration.
Still, recent drug arrests have highlighted the border's porousness. President Barack Obama and Prime Minister Stephen Harper signed a Feb. 4 agreement to better coordinate information and cross-border investigations.