Emergency crews received a call around 12:30 Saturday after a dog fell through the ice on Grenadier Pond in High Park.
Toronto Fire Captain Michael Westwood says the owner was crawling on the ice, attempting to pull the dog out, when crews first arrived.
At that stage, a marine officer went into the water and rescued the animal. Firefighters then resuced the officer after he became submerged.
Dog and owner are expected to be okay.
Three people -- dog-owner, officer, and one firefighter -- have been transported to hospital for hypothermia treatment.
Toronto emergency personel advise keeping at least 10 feet clear of shorelines during this spring thaw.