They were in a boat searching for a body that some local children thought they had spotted in the water the night before.
Sûreté du Québec Sgt. Daniel Thibaudeau said at about 5:15 a.m. the search team hit an area of the river where there was a strong current and the boat flipped over near the Masson Bridge.
After about 20 minutes in the water, the team was rescued. An officer was passing by on the bridge heard their screams and went to help.
"He managed to pull them out with some equipment and effectively saved their lives," said Thibaudeau.
Thibaudeau said three of the firefighters and the SQ officer are being treated for hypothermia, but their lives are not in danger.
He said the search for the body will resume later today.