The man, in his 40s, was with four others on a raft when it overturned, according to emergency personnel. The rest of the group made it to shore.
A group of people in a second raft found the man unconscious downstream.
EMS tried to resuscitate him, but he died on scene.
Everyone was wearing life jackets.
The incident happened on the Highwood River, about five kilometers west of Longview, Alta., off of Highway 41, said STARS Air Ambulance spokesperson Cam Heke.
STARS was called in case the man needed to be flown to hospital.
Longview is approximately an hour and a half southwest of Calgary.
RCMP on scene said the river is really dangerous.
Bridge jumping accident near Cochrane
Another man is dead after jumping off a bridge at Ghost Lake, near Cochrane.
Recreational divers pulled the man out of the water and took him to shore. He was in life-threatening condition when emergency crews arrived.
STARS was on scene to transport him to a Calgary hospital, but the man died at the lake.
The initial request for an air ambulance to do an aerial search for a missing person was made just before 5:15 p.m. MT.