FIRE ripped through 20,000 square metres of forest near Llyn Brenig.
North Wales Fire and Rescue Service was called to the incident on Sunday afternoon.
The blaze has now been extinguished - with over 20,000 square metres of trees and undergrowth near the reservoir being burnt in the fire, the fire service said.
A witness said: "Went up to the Brenig and driving along noticed some people had lost control of a fire by the lake - not sure how it was started, but it was spreading quickly.
"By the time we had turned around in the car it had reached the road going around the Brenig where people were walking and cycling with kids.
"You couldnt see due to the smoke. We got through but soon after it spread accross the road into the trees higher up with the wind driving it. Three fire engines were trying to control it."
More will follow on this story.
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