The woman clung to shore ice about 120 feet from the brink of the Horseshoe Falls on the Canadian side of the falls until she was hoisted to safety by rescue workers Monday evening.
Three Niagara Falls, Ontario, firefighters made the rescue.
Fire department officials said the woman had been in the water for more than an hour.
The woman was taken to Niagara General Hospital. Her condition isn't available.
A Niagara Falls visitor told The Buffalo News that he spotted the woman sitting on the ice with her feet in the water. He yelled to her, and she slid into the water, hanging onto the ice. He then called 911.