Crews are struggling to extinguish a stubborn fire that has been burning since Saturday in a dried-out swamp north of Stratford.

Officials say the fire is now burning underground and has consumed just under an acre of the 22-acre Ellice Swamp, located in a relatively inaccessible area. 

Not much smoke is visible, but officials say the fire is being fueled by a layer of peat moss, which is very flammable when dry.

“This fire is particularly difficult to fight because it is in the soil,” said land management technician Brandon Williamson. “It can last and sit there smoldering for weeks and months even depending on how much rain we get.”

The swamp, which is the largest natural area in Perth County, has had low-water levels due to drought-like conditions.

The Perth East Fire Department is on scene and planned to bring in several tankers of water to help control the fire.

Crews from the Upper Thames River Conservation Authority have also been working deep inside the swamp to extinguish the remaining hot spots.

They have been digging trenches and cutting down trees to prevent the fire from spreading.

"The problem was (Tuesday) it was dry and very windy and that caused a little increase on the perimeter and that’s why we have the tankers … working hard to get water in there,” said UTRCA communications manager Steve Sauder.

The smoldering area is about one kilometre from Line 46. Officials estimate 4,000 feet of fire hose is required to access the site, which is far from inhabited areas.

The cause of the fire remains unknown.

With reporting by Tyler Calver