SEATTLE (Reuters) - Potentially harmful human-caused noise pollution affects nearly two-thirds of all protected areas in the United States, according to a report released on Thursday.

Researchers found that 63 percent of all U.S. protected lands are exposed to manmade noise from cars and activities like mining that is at least as twice as loud as ambient sounds from natural sources like wind, according to Colorado State University and the U.S. National Park Service.

“What we found was that a lot of the protected areas in the U.S. are pretty noisy,” said George Wittemyer, a professor at Colorado State University who oversaw the research. Wittemyer called the findings “concerning.”

Along with well-known risks to humans from noise pollution, ranging from increased stress and lack of sleep to shortened life spans, increased noise levels can harm wildlife by masking natural noises and interfering with how animals hunt and mate, Wittemyer said.

The study included city and county parks, state and national forests, and national parks, monuments and refuges. Away from urban areas, the most common sounds were from cars, aircraft, and resource extraction activities like mining, logging and drilling, according to the study.

To chart noise levels, researchers used machine learning programs to analyze sources of both human and natural sound, predict how far those sounds would travel, and ultimately map out where human sounds are louder than natural noise created by things like flowing rivers. Wittemyer said the approach hasn’t been tried before.

Noise pollution can be especially hard to tackle, Wittemyer added, because not only is it invisible, it also tends to increase slowly over time, as noisy infrastructure like airports and roads get busier.

“As society grows, the sound level does, too,” Wittemyer added. “It’s just this sort of constantly increasing pressure.”

Wittemyer said the 37 percent of protected land not affected was spread evenly across the country, meaning a quiet nature spot is within reach of most Americans.

“Next time you go for a walk in the woods, pay attention to the sounds you hear -- the flow of a river, wind through the trees, singing birds, bugling elk,” Rachel Buxton, lead author and post-doctoral researcher in the Warner College of Natural Resources, said in a statement. “These acoustic resources are just as magnificent as visual ones, and deserve our protection.”