As North America’s tallest mountain, Denali has always been a challenge to climb. Those who dare to scale the Alaskan summit may be forced to dodge avalanches, bears, and altitude sickness—and piles of melting poo could soon be added to the list.

As USA Today reports, decades-old feces left behind by climbers could start thawing out as early as this summer due to climate change. Researchers say 66 tons of frozen poo has been dumped in snow pits or crevasses, according to estimates based on the average human “deposit.” That waste can eventually work its way downstream and end up on the surface of a glacier.

Situated in Denali National Park, the mountain—formerly known as Mount McKinley—rises to an elevation of 20,310 feet above sea level. That makes removing the waste difficult, but climbers are starting to embrace more sustainable practices. Companies that arrange expeditions at Denali have voluntarily offered to make their clients pack up and carry their own waste. Visitors were already required to carry their waste while climbing up the first 14,000 feet of the mountain, but the new measure would help protect the upper section of Denali as well.

“Climbers and particularly guide services are really embracing the new policy and are even exceeding it,” Michael Loso, a National Park Service (NPS) glaciologist, told USA Today. “It has become kind of an informal badge of merit to carry off all your waste.”

Of course, the softening poo is representative of a much larger issue. Some of Denali’s glaciers are melting at a rate that is concerning. The NPS has used comparative photography to measure some of the glaciers and concluded that most of the ones they studied had “retreated, thinned, or stagnated.”

Alaskan parks in general have also seen their ice-covered areas shrink by 8 percent in the last 50 years. “We have lost more glacier cover in the Alaskan national parks than there is area in the whole state of Rhode Island,” Loso said.

[h/t USA Today]