Yellowstone National Park is known for its geysers, hot springs and otherworldly landscapes. But beneath the spectacular views is a less visible problem: visitors regularly leave behind objects that can end up in the park’s fragile hydrothermal features.
The impact of this debris can go far beyond making the park look untidy. According to the National Park Service, Morning Glory Pool in the Upper Geyser Basin changed color during the 20th century, partly because visitors threw trash and other objects into it.
As Smithsonian Magazine has reported, before the 1960s, Morning Glory Pool was a deep blue, sometimes described as having a tropical appearance. Over time, however, the pool developed a distinctive green color with orange and yellow edges. Visitors had reportedly thrown pennies, rocks and other garbage into the pool over the years.
A report by Science Friday explained that the debris may have clogged parts of the heat source beneath the water's surface, potentially lowering the pool's temperature. That change created conditions that were more suitable for photosynthetic microorganisms that may not have lived there previously.
The Morning Glory Pool story illustrates why even seemingly harmless objects can be a problem in Yellowstone's hydrothermal areas.
Bizarre trash found at Yellowstone
In 2026 alone, Yellowstone's Geology Team had removed more than 20,100 pieces of trash, 5,600 rocks and sticks, and more than 280 hats from hydrothermal areas by early September, according to the National Park Service. Some of the objects are ordinary pieces of litter. Others are so unusual that it is difficult to imagine how they ended up in a hot spring or geyser.
Park staff have used different methods over the years to remove debris. At one point, Morning Glory Pool was partly drained to make it easier to retrieve objects that had accumulated inside.
