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Last fall, scientists from the Environmental Protection Agency (EPA) revealed that a popular lake in Wyoming’s Wind River Range is contaminated with human feces. And not just contaminated, but the most heavily contaminated lake out of nearly 1,000 lakes surveyed across the United States.

Look up a picture of Lonesome Lake, and you may be surprised. It doesn’t look like a biohazard. At first glance, it seems like paradise. The alpine lake sits at around 10,000 feet in elevation, and is ringed by the —a picturesque semi-circle of 12,000-foot granite spires that has long enchanted rock climbers and trekkers alike. It’s also a stone’s throw from the Continental Divide Trail and a common stopping point for long-distance hikers. As a result, it is among the most heavily-trafficked backpacking destinations in the region. During peak season in August, as many as 400 hikers may visit the Cirque of the Towers each week.

In the spring of 2022, as part of the EPA’s , the agency collected samples of water from 981 lakes around the country, including Lonesome. The results, published last fall, show that Lonesome Lake contains 490,895 calibrator cell equivalents of the bacteria genus Enterococci for every 100 milliliters of water, the highest of any lake tested. The EPA’s safe limit for swimming—not just drinking, mind you, but swimming—is 1,280 per 100 milliliters, meaning the contamination in Lonesome Lake is a jaw-dropping 384 times higher than the recommended limit.

As noted by local nonprofit news outlet , “Arguably, Lonesome Lake was the most spectacular, remote waterbody in the broad study examining lake health all around the United States … and yet the data also suggested that Lonesome Lake’s water was the most polluted by poop. That’s especially remarkable given that the assessment also looked at lakes and ponds in urban areas and agricultural regions more typically associated with feces-related pollution.”

It’s worth noting that high concentrations of Enterococci do not necessarily equate one-to-one to high concentrations of feces. Researchers say more work still needs to be done. “A single datapoint doesn’t necessarily tell us much of anything,” the DEQ’s Ron Steg told WyoFile. “We need to get some real data to understand if there is a problem. If there is, we’ll react to the results of the data.”

Enterococci is intestinal bacteria, and thus its presence in a water supply is a strong indicator of fecal contamination. The sampling at Lonesome was conducted through the Wyoming Department of Environmental Quality (DEQ), and when the results came in last fall, researchers from the DEQ and U.S. Forest Service went out to take additional samples at the lake, this time searching for another indicator of fecal contamination, Escherichia coli, but came up with nothing. Over the next two months, at Lonesome Lake and nearby Big Sandy Lake, another popular trekking destination, to get a more definitive picture of the degree of contamination.

But to those in the know, the study results come as no surprise. “I tell people definitely do not swim in there, I tell people definitely do not drink the water,” Brian Cromack, a local outdoor gear shop employee, told WyoFile. “It’s been heavily contaminated for a long time, just via the negligence of outdoor recreation enthusiasts over the years.”

Although they may look pristine, alpine lakes surrounded by granite peaks like the Winds can face higher levels of contamination, because the non-porous granite and thin soil create a “bathtub effect,” offering no natural filtration for water. This, combined with the steep gradients, means that rain and snowmelt quickly wash fecal matter—not just from humans, but from dogs and natural wildlife—from the surrounding slopes down into the low-lying lakes. This problem peaks during spring thaw, when months of waste frozen in snowpack are often flushed into the water all at once, coinciding with peak visitation periods in the summer. At high elevations, cold water temperatures also allow dangerous pathogens like Giardia and E. coli to survive for longer periods.

It remains to be seen what the follow-up studies will reveal at Lonesome Lake, or what is to be done about it. Other high-traffic wilderness locales, like California’s Mount Whitney Zone, now require all visitors to pack their waste out in a “wag bag.” Currently there is no specific stipulation on how to dispose of bodily waste in the Cirque of the Towers, aside from following basic Leave No Trace principles—bury waste in a hole six inches deep, 200 feet from trails and water sources. But research is increasingly indicating that, taking into account the growing number of people recreating in the wilderness, these practices actually are no longer enough to prevent fecal contamination.