NACHES, Wash. — Hikers visiting Boulder Cave this summer may be surprised to find a most unnatural shade of green in the National Forest — astroturf.

The entrance of the cave is now carpeted in the artificial stuff as part of the Naches Ranger District’s new program to protect the cave’s bat population from the devastating disease that’s killed about 6 million bats nationwide in the past decade.

It’s part of a new safety protocol the district designed quickly this spring after an infected bat was discovered in North Bend in March — the first known case of white nose syndrome in the western U.S.

The disease hasn’t been recorded in Boulder Cave and officials want to keep in that way – it’s the winter home for one of Washington’s largest populations of the rare Townsend’s bat.

“We know (white nose syndrome) is spread by humans, bats typically don’t migrate as far as the disease has moved so quickly,” said interpretive ranger Janell Shah, who started her cave protection job three weeks ago.

“It’s a fungus disease and it spreads via spore, so when you are walking in a cave then you are picking up the spores on your shoes and clothes,” she explained.

Shah stands near the mouth of the cave to explain the disease and ask people to use boot cleaning brushes and walk across the astroturf on their way into the cave. It’s a “decontamination station” designed to remove any fungus spores an unsuspecting hiker might be carrying from other caves.

Every night, Shah sprays down the boot brushes with alcohol and takes the astroturf down for washing in bleach. She also asks visitors to thoroughly clean their clothes and shoes when they get home, to prevent unwittingly carrying the fungus to another cave if it sneaks into Boulder Cave.

The disease, caused by a fungus which can make a bat’s nose, wings, and ears look fuzzy white as it causes internal damage, kills 99 percent of infected bats, according to the U.S. Fish and Wildlife Service. It can wipe out entire colonies as the bats hibernate.

“We are extremely concerned about the confirmation of WNS in Washington state, about 1,300 miles from the previous westernmost detection of the fungus that causes the disease,” said U.S. Fish and Wildlife Service Director Dan Ashe in a news release about the North Bend discovery in March.

“Bats are a crucial part of our ecology and provide essential pest control for our farmers, foresters and city residents, so it is important that we stay focused on stopping the spread of this fungus,” Ashe said. “People can help by following decontamination guidance to reduce the risk of accidentally transporting the fungus.”

The 25,000 year old cave is one of the most popular places on the Naches Ranger District and so it’s important to balance access with protection for the bats, said Bill Zimmer, the district’s recreation supervisor.

“It’s the only cave on this side of the mountains these bats use,” he said. “We want to protect the bats and we don’t want to shut this place off to people.”

Shah said that so far, people seem happy to clean up their shoes to protect the bats.

There’s no evidence yet if Townsend’s bats are susceptible to white nose syndrome, but two of Washington’s more common bats, the Little Brown Bat and the Big Brown Bat, are among the species known to be susceptible to the fungus.

The state Department of Fish and Wildlife says more research is needed to understand which of the state’s 15 bat species are most at risk. The agency is asking residents to report any sick, oddly behaving, or dead bats online here.