Fish, wildlife and ultimately people could be exposed to harmful levels of toxic chemicals in the waters of the Colorado River that flows through the Grand Canyon, according to a new study led by the U.S. Geological Survey.

The study, published last week in the scientific journal Environmental Toxicology and Chemistry , found that concentrations of mercury and selenium in the Grand Canyon's food webs – the interconnected food chains that exist within an ecosystem – regularly exceeded levels considered risky for consumption by fish and other animals.

Researchers from USGS surveyed six sites spread out over a 250-mile stretch of the Colorado River within the Grand Canyon, downstream from the Glen Canyon Dam, and found potentially harmful concentrations of the chemicals "in everything from bugs to trout to algae," United Press International notes .

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/1280-GettyImages-474898258_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/1280-GettyImages-474898258_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/1280-GettyImages-474898258_0.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > A view of the Colorado River from the Navajo Bridge near Marble Canyon, Arizona, on May 18, 2015. (Mladen Antonov/AFP/Getty Images) (Mladen Antonov/AFP/Getty Images)

The presence of the toxic chemicals in a place like the Grand Canyon – "one of the most remote ecosystems in the United States," the USGS points out – shows the far-reaching impacts that the industrialized world has on even largely well-preserved environments like our national parks.

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"Managing exposure risks in the Grand Canyon will be a challenge, because sources and transport mechanisms of mercury and selenium extend far beyond Grand Canyon boundaries," said Dr. David Walters, a USGS research ecologist and the study's lead author, in a press release .

One of the most important transport mechanisms for mercury is a type of algae that flows into the Colorado from Lake Powell. This algae, which carries high amounts of a bioavailable form of mercury , is eaten by blackflies, which in turn are eaten by trout in the river.

"We think [the mercury] is getting picked up by that algae in Lake Powell and exported into Grand Canyon," Ted Kennedy, a USGS researcher at the Grand Canyon and one of the study's co-authors, told the Arizona Daily Sun .

Most of the mercury that makes its way into the Grand Canyon comes from the atmosphere , the study notes, from manmade sources like gold mines and coal-burning power plants as well as naturally-occurring mercury that's already in the air. It can also come from power plants as far away as California or even Asia, drifting throughout the atmosphere for months after it is emitted.

Selenium, on the other hand, largely enters the Grand Canyon ecosystem thanks to the irrigation of selenium-rich soils in the upper Colorado River basin, the USGS says .

Exposure to high levels of mercury and selenium "has been linked to lower reproductive success, growth, and survival of fish and wildlife," USGS notes , and ultimately can be harmful to people if they consume fish and animals that contain risky amounts of these chemicals.

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Surprisingly, the study's authors said they didn't find patterns they expected to find with mercury in rainbow trout in the canyon. Thanks to a process called biomagnification, larger fish usually have higher concentrations of mercury than smaller fish in an ecosystem.

"But we found the opposite pattern, where small, 3-inch rainbow trout in the Grand Canyon had higher concentrations than the larger rainbow trout that anglers target," the USGS noted in a press release .

While the study hasn't prompted the National Park Service to issue any consumption advisories for fish caught in the Grand Canyon, the authors said they plan additional studies to better gauge the risk to humans from the animals there.

Read the full study at Environmental Toxicology and Chemistry here .

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