Amid both the national conversation about water pollution following the Animas River spill and a controversial debate over whether to tighten laws within the Clean Water Act, a recent U.S. Geological Survey study found that human activity is causing an alarmingly high concentration of toxins in one of our most important ecosystems.

The study, published in the scientific journal Environmental Toxicology and Chemistry, found mercury and selenium in the Grand Canyon segment of Colorado River at concentrations “sufficient to pose exposure risks for fish, wildlife, and humans.”

As the authors of the study write, the findings show that even remote areas like the Grand Canyon “are vulnerable to long-range transport and bioaccumulation of contaminants.” This confirms what environmentalists have worried about for decades and adds a new element to the conversation about water pollution and protection.

The scientists tested six areas downstream from the Glen Canyon Dam, which forms Lake Powell, and found that elevated concentrations of both toxins in all sites regularly exceeded levels considered safe. At high concentrations, mercury and selenium become two of the “leading causes of impairment of lotic ecosystems” – ecosystems with flowing bodies of water.

Mercury and selenium “pose widespread and persistent exposure risks to aquatic organisms and the terrestrial animals that feed on them,” states the study. And “exposure to high levels of [the elements have] been linked to lower reproductive success, growth, and survival of fish and wildlife.”

In humans, long-term exposure to mercury is known to cause neurological and developmental problems – who can forget the Mad Hatter in Alice in Wonderland? – while the effects of chronic exposure to selenium are not as well known. That being said, according to the EPA, “the consumption of high levels of selenium in the diet by pigs, sheep, and cattle has been shown to interfere with normal fetal development and to produce fetal malformations.”

Now that scientists know these elements are in the water, the next step is to figure out a way to manage the risks of exposure. It’s something David Walters, USGS research ecologist and lead author of the study says “will be a challenge, because sources and transport mechanisms of mercury and selenium extend far beyond Grand Canyon boundaries.”

Though the exact source of the contaminants is unknown, mercury typically enters a remote aquatic ecosystem like the Grand Canyon through the atmospheric deposition of fossil fuel emissions and watershed runoff – though pollution-causing algae blooms from Lake Powell could be another source — while selenium typically comes from coal ash and irrigation projects that deposit selenium-rich soils upstream.

The study names the coal-fired Navajo Generating Station and other upstream industrial and agricultural endeavors as the likely culprit of these toxins, but suggests further tests be conducted.

Sandy Bahr, chapter director of the Arizona Sierra Club, echoes this sentiment, albeit a little more directly: “The U.S. Geological Survey’s report singled out coal-fired power plants, in particular the Navajo Generating Station located near the canyon, as one of the potential sources of this dangerous contamination.”

She says the Sierra Club is calling for “an immediate and in-depth investigation into the connection between coal plant pollution and the mercury contamination at Grand Canyon [because] when mercury pollution is put into the air and water, it spreads out into the environment and causes damage to human and environmental health as it moves up the food chain.”

While the study cautions that mercury and selenium “could be harmful if eaten by fish, wildlife, and humans,” the EPA has not issued any human consumption advisories for fish caught in the area.

And according to Ted Kennedy, USGS researcher and one of the study’s authors, the findings of the study weren’t an all-out harbinger of doomsday for the environment: “The good news is that concentrations of mercury in rainbow trout were very low in the popular Glen Canyon sport fishery, and all of the large rainbow trout analyzed from the Grand Canyon were also well below the risk thresholds for humans.”

The publication of this study, which took years to execute, comes at a very interesting time in the American political scene, as many are talking about water pollution.

Less than one month ago, the EPA accidentally released more than 3 million gallons of wastewater into the Animas River, fomenting a national conversation about federal laws that govern the clean up of mining sites, and who exactly is responsible for dealing with the cleanup problems. And just last week, a federal judge in North Dakota issued a 13-statewide injunction against the EPA’s new Clean Water Rule, citing federal overreach.

Arizona U.S. Senator John McCain, Arizona's attorney general, and the Arizona Farm Bureau — among others — are celebrating the injunction and calling water regulation a states' rights issue. But critics fear this is another example of both putting industry above the environment, and of what Bahr calls “a knee-jerk reaction against whatever the EPA proposes.”

So as issues like contaminated drinking water and the bioaccumulation of heavy metals — whether from a breeched mine or coal-fired power plant — clearly are having their moment in the spotlight, Bahr thinks we should look at the USGS study and realize how critical it is that we “focus on preventing pollution and recognize weakening, delaying, and de-funding of environmental protections has real costs.”

Because at the end of the day, “If we, as a country can't step up to protect Grand Canyon, what will we protect?”

Read the full study below: