Steve Blake, visitor safety specialist at the park, says the man and a friend had been on a trail about 40 metres from the viewing area where tourists congregate to marvel at the power of the water cascading over the rocks.
The friend frantically called 911 as the man was swept over the falls.
Both are believed to be from the Edmonton area.
Blake says search teams looked for the man Thursday night and all day Friday with no success.
He says the search will continue Saturday, but that will be the last formal operation.
"Then we'll just be doing periodic searches after that."
Blake says the last time someone fell over the falls was in 2006.
"That was somebody who intentionally climbed over the fence," he says.