ISLE ROYAL, Mich. (AP) — A wildfire on Michigan’s remote Isle Royale has been about 15% contained and crews have saved some historic cabins from encroaching flames, an official said Wednesday.

The fire began Aug. 10, apparently sparked by a lightning strike on the drought-stricken wilderness island, said Liz Valencia, a spokeswoman for Isle Royale National Park.

“It’s extremely dry on the island, so it probably didn’t take much,” she said Wednesday.

The wildfire on the 571,000-acre Lake Superior island has left a little over 200 acres either scorched or still burning, Valencia said. Crews are not actively fighting the fire, but they are monitoring the flames to make sure they don’t threaten any park infrastructure, she said.

“It’s moving very slow right now,” Valencia said.

The National Park Service closed some trails and campground areas after gusty weekend winds quickly increased the size of the fire, which is burning on the northeastern end of the island.

The fire’s rapid spread prompted fire crews on Monday to use special planes to collect water from Lake Superior to douse flames and protect some historic cabins dating to the early 1900s on a small island within the park’s Tobin Harbor. But flames did destroy one outhouse, Valencia said.

Isle Royale is part of Michigan but is 15 miles from the Minnesota shoreline. It’s a popular destination for outdoor enthusiasts for hiking and backpacking.

Meanwhile, U.S. Forest Service officials on Wednesday extended the closure of the Boundary Waters Canoe Area Wilderness after Minnesota’s largest wildfire doubled in size.

The Greenwood Lake fire burning in the Superior National Forest in northeastern Minnesota grew to about 30 square miles Monday, and four new smaller fires ignited within the BWCA. By Wednesday, the size was estimated at 34 square miles.

Forest officials decided to keep the popular wilderness closed another week, to Sept. 3, dealing a blow to tourists who spent months planning their trips there and to the outfitters and other businesses serving the 1 million-acre Boundary Waters.

On Wednesday, officials also closed Forest Service lands along the scenic upper Gunflint Trail, a dead-end paved road deep into the wilderness, including the Trails End and Iron Lake campgrounds and the Magnetic Rock Hiking Trail. The closure will last at least a week.