A teenager was pinned for hours and was nearly unconscious for a time as rushing waters trapped his leg between his damaged canoe and rocks after he descended a waterfall near the Minnesota-Canadian border, authorities said Wednesday.

Rescue personnel freed the injured 15-year-old at the bottom of Upper Basswood Falls late Tuesday afternoon, but it was another two-plus hours before the teen was airlifted out of the Boundary Waters Canoe Area Wilderness (BWCA) by a State Patrol helicopter and eventually taken to a hospital in Ely, Minn.

The teen, whose name has not been released, was being treated Wednesday for “crushing injuries” to a leg and hypothermia, said Lake County Sheriff Carey Johnson.

“They were afraid they were going to lose him,” Johnson said of two fellow canoeists who came away unscathed when they went over the 25- to 30-foot falls late Tuesday morning. The teen and his companions were in one of at least four canoes from a church group in Rochester, the sheriff said.

The force of the cascading waters pressed the mangled canoe against the teen’s leg, pinning him on the rocks, Johnson said.

Upper Basswood Falls “is one of the most dangerous places” in the BWCA to navigate, he said. It is a tempting place for canoeists and boaters to catch a thrill, rather than portage around it, he said.

The sheriff said he has heard a “couple of different stories so far” about whether these canoeists intended to ride down the falls, which Johnson described as a series of rapids.

Rescuers determined that the teen became trapped sometime between 10:30 and 11:30 a.m., but the lack of cellphone service in the area kept them from calling for help.

Shortly after 1 p.m., a group with the Boy Scouts’ Northern Tier High Adventure Program that was doing portage trail maintenance came upon the teen and radioed into its base on Moose Lake. From there, a call to 911 was made.

The waters where the canoeist got stuck are “more like a rapids on steroids,” said Northern Tier General Manager John Van Dreese.

Sheriff’s personnel reached the teen about 3 p.m. Tuesday and began treating his leg injuries. Emergency personnel freed him around 5:15. He was “nearly unconscious during the last 30 minutes of the rescue and was suffering from extreme hypothermia,” according to the Sheriff’s Office.

The State Patrol helicopter dispatched from the Twin Cities lifted the teen out around 7:30 p.m.

“We couldn’t land anywhere near” the teen, said the State Patrol’s Greg Burgess, the pilot. “We packed the victim up and took him a half-mile to an opening in the woods” for the rendezvous with a U.S. Forest Service seaplane, Burgess continued. “It was the only way to get him out.”

Justin Mayne, a captain with the Lake County Rescue Squad, said recent rains would have made the water’s flow more forceful. The airlift was complicated because it was staged “in such a remote area,” he added.

Mayne described the falls as “kind of like a long chute. People do canoe it. It’s not like a straight falls.” Even with his own experience as a rescuer, Mayne said, “You won’t catch me doing that for fun.”

A similar rescue in the same area was pulled off in June 2014 when several Boy Scouts and their leaders from suburban Cincinnati were canoeing on stormy Basswood Lake.

One canoe was pushed to the shore by the relentless winds and waves, while the other capsized. Two of the leaders were rescued by a State Patrol helicopter from an island in the lake.