A wildfire that forced 80,000 people in northern Alberta to flee more than a year ago has finally been extinguished.

Wildfire information officer Lynn Daina says the Horse River fire that started on May 1, 2016 and destroyed more than 2,400 buildings in Fort McMurray and area was deemed officially out on Aug. 2.

She says they had to wait for winter to be over to see if any smoke or heat remained from the massive fire because it was so fierce and unpredictable.

Daina says they also used advanced heat detectors from helicopters to ensure there were no remaining hot spots coming from the ground. Wildfire crews will continue to monitor all areas.

The fire spread into Saskatchewan and burned nearly 6,000 square kilometres in total.

"With a fire that size it takes time to make sure it is fully extinguished so we wait for a winters worth of snow and then in the summer we check to see if any smoke pops up and if not we use advanced heat detectors from helicopters and make sure there is no remaining heat," Daina said.

"Once we determine there is no remaining heat left on the fire, we determine it is extinguished and out."

The fire caused an estimated $3.8 billion in insured damage.