Geologists in Yellowstone National Park are reporting an unusual threat to the area’s hydrothermal areas. According to a report from the U.S. Geological Survey (USGS) observatory, lost hats are infiltrating the park’s hot springs, geysers, mudpots and fumeroles.
The park’s specially trained Geology Program is charged with cleaning up more than 10,000 iconic hydrothermal areas in Yellowstone National Park, including Grand Prismatic Spring and Old Faithful. The team is constantly battling a daunting array of human litter—in 2025 alone, they have already collected “more than 13,000 pieces of trash, 4,000 rocks and sticks, and over 300 hats.”
These aren’t just dollar-store hats either. The USGS estimates that headwear collected this year is worth over $6,000.
Trash floating in Yellowstone’s pristine pools is more than an eyesore. It also poses a serious risk to the delicate ecosystems inside these hydrothermal features.
“Debris thrown into a hot spring can irreversibly change its behavior, resulting in lower temperature, changes to color, and altered eruption behavior,” wrote the USGS in a report published on September 8.
Located just over a mile from the Old Faithful Visitor Center, the park’s famous Morning Glory Pool is one such example. It was named in the 1880s for its resemblance to the blue flower, but changed hues over the years to shades of oranges, yellows and greens. Although features shift naturally over time, park officials have reason to believe that humans have caused the stark shift by throwing coins, trash, and other debris into it, blocking the movement of hot water into the pool and altering its temperature.
Removing all this trash isn’t an easy task. Staffers can’t simply swim into the boiling springs and pluck debris out with a net. Rather, the team uses a hodgepodge of tools, some of which are custom-made by the park with a “little more than creativity and elbow grease.” This array of trash-picker-uppers includes fishing rods, extra-long slotted spoons, and grabber poles up to 30 feet long. The USGS added that in total, pool cleanup efforts this year have required the team to walk over 1,300 miles and drive more than 11,000 miles around the park to various hydrothermal areas.
Yellowstone’s trash problem is largely accidental, according to the USGS. With more than 4.7 million visitors in 2024, it’s one of the most visited national parks in the United States. This large number of people, combined with the park’s frequently high winds, means that personal items often are blown into the park’s hydrothermal areas.
However, some of the litter is intentional, like biodegradable items such as sunflower seed shells and orange peels. While visitors may think these items are harmless, the USGS notes they are damaging to the pools and “particularly time-consuming for the team to remove.”
USGS team members recover more than a few wacky items from the pools now and then.
“Favorite finds from the team during the summer of 2025 include a Birkenstock sandal, a pizza box with slices still inside, a fake Louis Vuitton bucket hat, a stuffed koala toy, a ball cap with the phrase ‘I PEE IN THE LAKE,’ and a Polaroid picture of Excelsior Geyser—which was found within Excelsior Geyser’s crater,” wrote the USGS.
While these discoveries are sometimes humorous, the USGS hopes such items remain with their owners, and offers a few simple reminders for park visitors.
“Hold on tight to your hats, stay on marked boardwalks and trails, and make sure all your trash (even the food!) ends up in a trash can,” wrote the USGS.
The post What’s the Latest Threat to Yellowstone’s Geysers? Hats. appeared first on Outside Online.
