Two fires burning inside the Bob Marshall Wilderness are sending smoke into the Flathead Valley. The largest - a fire first detected on Tuesday, Aug. 16, near Big Salmon Lake - quickly grew to about 2,000 acres by Thursday, Aug. 18.

Spotted Bear and Jumbo lookouts first spotted the Big Salmon Lake Fire near the north shore of the lake, which is inside the wilderness east of Holland Lake, and initially estimated it at 10 acres.

Aerial observers reported the fire at 100 acres by Wednesday afternoon and actively burning. By early evening, the fire was estimated at 730 acres, and by Thursday the estimate was 2,000 acres.

"This is a location where we would not have wanted to have a fire," Spotted Bear District Ranger Deb Mucklow said. "We're developing plans that will account for firefighter safety."

The trail to Big Salmon Lake, a well-used access into the wilderness for packers over Holland Pass, and the Lime Creek trail have been closed due to the Big Salmon Lake Fire. Structure protection efforts are planned for the Salmon Forks cabin, Salmon Forks suspension bridge and the Little Salmon Bridge.

Meanwhile, the lightning-caused Hammer Creek Fire is burning along the South Fork Flathead River about 2 1/2 miles north of the Big Prairie Ranger Station. It grew from 248 acres to an estimated 500 acres by Thursday as a result of dry, warm weather and gusty winds.

The Hammer Creek Fire is mostly being allowed to burn to the east for resource benefits in the wilderness. Suppression actions have been necessary to keep the fire from crossing to the west side of the South Fork River, which could force the closure of a busy west-side trail, Mucklow said.

A trail following the east side of the South Fork has been closed north of Big Prairie, and structure protection measures have been taken at the Big Prairie Ranger Station and a nearby pack bridge.

Outside the wilderness, the human-caused South Fork Lost Creek Fire gained ground in steep, forested terrain seven miles southeast of the community of Swan Lake. The fire grew from 520 acres on Tuesday to more than 600 acres by Wednesday afternoon.

Firefighters were successful in cutting fire lines along the west and south flanks of the South Fork Lost Creek Fire, while helicopters conducted water drops at higher elevations. Five helicopters and about 190 people, including four hotshot crews, were working on the fire. The estimated cost of fighting the fire was nearing $1 million.