Niagara Parks Police said witnesses reported seeing the man climb over a railing next to the Horseshoe Falls at 10.20am on Monday and “deliberately jump” into the Niagara River.
Seriously injured, he surfaced in the lower Niagara River basin near the Journey Behind the Falls observation platform and managed to make it to the shore on his own.
“He waded ashore,” said platoon chief Dan Orescanin of the Niagara Falls Fire Department. “He must have gotten swept into an eddy, floated over there and was able to get out on his own.”
Mr Orescanin said the man was conscious and talking at first, but went quiet. He appeared to have chest injuries, including broken ribs and a collapsed lung.
The man was airlifted to Hamilton General Hospital with what police initially said were life-threatening injuries.
Hospital spokeswoman Agnes Bongers said the man was critically injured but expected to survive.
Horseshoe Falls, on the Canadian side of the river, is the tallest of the three main falls, higher than the American Falls and Bridal Veil Falls.
The man, believed to be in his 30s or 40s, was rescued two hours later after fire department rescuers abseiled down the steep and rocky gorge and pulled him in a basket back up the cliff.
“It was very difficult, between the shale and the boulders, and everything is wet and slick. It’s slimy,” Mr Orescanin said.
About seven rescuers struggled to carry the basket up to a point where it could be lifted with ropes suspended from an aerial truck.
“We had to basically hand-carry him, a foot at a time, up the rope,” the chief said.
Although several people have survived trips over the falls in barrels or other contraptions, beginning with Annie Edison Taylor in 1901, few have survived unprotected.
In 1960, seven-year-old Roger Woodward was swept over the falls wearing a life jacket and survived.