Christian Therrien, 62, and son Sebastien were combing through waist-high wild grass last week near Fernie when they spotted the enormous puffball mushroom, the Fernie Free Press reported.
"There was lots of laughing and screaming," Therrien said. "I've found a lot of 5- and 10-pound mushrooms, but when I came upon this one I was shocked."
He took the giant fungus home to weigh it and said he would return it to where he found it so it could release its spores and perhaps create a new generation of jumbo Calvatia gigantea.
Therrien said the mushroom weighed about as much as an 8-year-old boy.
His wife Mimi said she was investigating to see if it might be a world record, the newspaper said.
In any case, Therrien couldn't have hosted a mushroom banquet, as puffballs are only safe to eat when they are very young and small, various agricultural and gastronomy Web sites said.