Canada's military was pitching in with helicopters and other assets to help local officials with rescue and evacuation efforts, Prime Minister Stephen Harper said.
The flooding was caused by a slow-moving storm that dumped 154 millimeters (more than 6 inches) of rain on the region from Wednesday to Thursday, CNN meteorologist Sherri Pugh said. As much as another inch of rain, about 25 millimeters, is possible northwest of Calgary on Friday, and yet another front is expected Monday, bringing the threat of more rain.
Calgary, near the Canadian Rocky Mountains, is perhaps best known for its rodeo, held each July. More than 1.4 million people attended last year, organizers say.
This year's Stampede events are due to begin in 13 days. It was unclear if the flooding would affect the event, but organizers did say on their website that other events scheduled at the park where the Stampede is held have been canceled through Sunday.
Calgary authorities are using the park as a staging area for flood response efforts.