RCMP say the 51-year-old victim was on the Kananaskis River Tuesday afternoon when she fell overboard and submerged for a short time.
She was pulled back onto the raft, but soon went into medical distress.
Others aboard tried to resuscitate her before emergency medical technicians took over.
She was taken to hospital in Calgary, where she was pronounced dead.
The woman's name has not been released and police are still investigating.