The campfire-sparked Interlaken wildfire, which continues to grow in Lake County and has reached a total burn area of 731 acres, is now 86% contained, fire officials said Sunday evening.

Flames — which have been burning on U.S. Forest Service land for seven days — may continue to creep outward, ,according to forest service reports.

On Saturday, the fire was only 15% contained at 591 acres. By Sunday morning, it was 45% contained at 592 acres and by Sunday evening, the fire was 86% contained. The burn area increased on Sunday to 731 acres as the north edge of the fire traveled toward the lake, according to an update posted on the Interlaken Fire Information Facebook page. Fire officials don’t expect the blaze to reach full containment until June 23.

“We’re expecting hot, dry, windy conditions for the next few days and it’s really going to test our containment lines,” fire officials told the Denver Post on Sunday.

And containment isn’t the end of the wildfire’s burn.

Wildfire containment isn’t the same as a fire being put out — it’s the status of a control line being completed around the fire to stop the fire’s spread. Wildfires can burn for days or longer after containment is reached.

While the fire’s growth is small compared with other Colorado wildfires, like the nearly 5,700 acre Spruce Creek fire started by a lightning strike in May, it’s not a small area overall.

Overnight Thursday, the fire grew 6 acres — about the same as four and a half football fields. As of Sunday evening, the fire is burning on about 553 football fields of land.

The fire was started by an abandoned campfire about 180 feet from the Interlaken trail and 1.5 miles from the trailhead,fire officials said.

Fire investigators believe the campfire was not properly extinguished and was burning for several days before it sparked the wildfire Tuesday afternoon. Abandoned fire coals, when not taken care of, can retain heat for extended periods and can reignite if winds pick up.

If the fire had started in late July or August, during a period of high fire danger, it may have grown to around 60,000 acres, fire officials said in a community brief on Saturday.

On Saturday morning, nearly 300 fire personnel were on scene at Interlaken, working to douse the flames and protect the area’s historic structures, fire officials said. None of the historic district’s buildings have been damaged.

An aerial video posted by forest service officials Saturday morning shows the spread of the fire and various burn intensities across different areas of Interlaken.

“Burn severity depends on the amount of fuels, the weather and the topography,” forest service officials said in a statement Saturday. “As you can see in the video, some areas burned very hot with high tree mortality, while in other areas the fire burned surface fuels and did not kill many trees.”

On the north side of the fire, the terrain is steep and full of dead and downed trees, forcing crews to establish a fireline further down the hill along Interlaken Trail and wait for the fire to come to them.

Local search and rescue crews are assisting firefighting efforts by using boats to bring supplies across the lake to the fire area, and more helicopters are expected to arrive to help douse the flames, fire officials said Friday.

Four helicopters dropped water and retardant on the fire over the weekend, officials said.

Interlaken was evacuated Tuesday. Pre-evacuation orders in place for Lake County’s Lost Canyon along County Road 30 and northern Chafee County were lifted Saturday evening. .

Temporary flight restrictions are in effect over the fire area to give room for fire crews to work — flying outside aircraft or drones in the area will impede firefighting efforts and ground fire crews’ aircraft, fire officials said Saturday.

Updated at 8:18 a.m. Monday, June 17, 2024: This article was updated to include new fire containment information.

Originally Published: June 15, 2024 at 2:47 p.m.