Authorities have ordered the evacuation of downtown Calgary as flooding has left swathes of the city underwater.
Torrential rain and floodwaters have washed away roads and bridges around Alberta's largest city and have caused landslides elsewhere in the province.
Both rivers that flow through Calgary, the Bow and Elbow, have flooded.
Canadian Prime Minister Stephen Harper is expected to tour flood-damaged areas later on Friday and has promised federal assistance.
The Elbow crested near the city earlier on Friday but Alberta Premier Alison Redford warned residents should be prepared for more flooding downstream.
Communities further south were under total evacuation orders; roughly half the homes in the town of High River were flooded.
While an estimated 230,000 people live and work in Calgary's downtown area, officials believed there would be few people to evacuate because many did not come into work on Friday.
Some 25 neighbourhoods in Calgary, a city of one million, had already been evacuated. An estimated 75,000 residents have been ordered out of their homes there.
The floods come after a rainy week in Alberta, capped by 4in (10cm) of downpour on Thursday.
Military helicopters rescued about 30 people off rooftops in the Calgary area. At least 350 soldiers are being dispatched to the flood zone, according to the defence minister's office.
The mountain resorts of Banff and Canmore were left isolated after the Trans-Canada Highway was closed.
One resident of Canmore said he awoke in the middle of the night to a "kind of rumbling" sound and realized it was the nearby creek.
"At first it was just intense, pretty powerful, amazing thing to watch," Wade Graham told the Associated Press.
"As daylight came, it just got bigger and bigger and wider and wider, and it's still getting bigger and bigger and wider and wider."
"I watched a refrigerator go by. I watched a shed go by. I watched couches go by. It's insane," he added.
Calgary Mayor Naheed Nenshi said about 1,500 people went to emergency shelters while the rest were staying with family or friends.
Mr Nenshi warned that although the Elbow had crested, the city was not yet out of danger.
The Bow river, which Mr Nenshi said looked like "an ocean at the moment", is expected to remain at its current level for the next 12 hours.
Police have advised people against travelling downtown, public transportation has been shut, and schools are closed.
Officials said lions and tigers from the Calgary Zoo may need to be transferred to prisoner holding cells at the downtown courthouse. The Saddledome, home to Calgary's professional hockey team, is also flooded with water levels rising to the stadium's 10th row.
Calgary resident Marshall Strong told the BBC several of his family members' homes were flooded.
"There's just so much going on, it's insane," he said. "One farm that we went to had 60 cattle drowned in the fields.
"It is truly unbelievable what has happened in such a short time. Calgary is a strong city and we have held it together better then we imagined."
No deaths have been reported, although one woman swept away in a mobile home is still missing.