Brain-eating amoeba detected at western national parks Coloradans love to visit

If a western national park road trip is on your summer bucket list — and let’s be honest, for a lot of us Coloradans it absolutely is — there’s a new study making the rounds that’s worth a quick read before you go. Spoiler: it involves brain-eating amoebas. Yes, that’s a real thing, and yes, they found them at some of our favorite parks.

A new federal study published by the U.S. Geological Survey and its partner agencies surveyed 40 thermally impacted recreational water sites across five western national parks and recreation areas. The findings? Researchers detected Naegleria fowleri — the microscopic organism known as the “brain-eating amoeba” — in about one-third of the samples taken. The parks that tested positive include three heavy hitters that Coloradans love to visit: Yellowstone National Park, Grand Teton National Park and Lake Mead National Recreation Area.

Specific spots where the amoeba was found include Yellowstone’s famous Boiling River, Lewis Lake, the Firehole River’s Goose Lake and the Firehole Canyon Swimming Area. Over at Lake Mead, four sites tested positive: Boy Scout, Nevada, Blue Point and Roger’s Hot Springs.

Before you cancel your camping reservations, take a breath. Infections are still extremely rare. According to the CDC, only 167 cases of PAM — the brain infection caused by the amoeba — were recorded in the entire United States between 1962 and 2024, and fewer than 10 people a year typically contract it. That said, the survival rate is grim: only four people out of those 167 cases survived, giving it a roughly 98% fatality rate.

Brent Peyton, a Montana State University professor and one of the study’s authors, put it plainly: “There is no need to be alarmed, but it is good to be aware. N. fowleri is found worldwide and is present across the United States, particularly in southern states. It inhabits hot springs, lakes, rivers, and has even been detected in tap water. However, N. fowleri infection can easily be prevented by keeping water out of one’s nose.”

That last part is key. The amoeba is not dangerous if swallowed — it becomes a problem only when contaminated water goes up your nose and reaches the brain. So that dunk-your-head-under-the-hot-spring move? Maybe skip it.

The National Park Service noted that signage is typically not posted at affected sites. Instead, visitors should simply assume the amoeba “can be present in warm freshwater bodies across the United States” and plan accordingly — especially in thermally heated waters like natural hot springs.

Researchers also flagged that cases could become more frequent as water temperatures continue to rise globally. So while this summer’s trip should still absolutely happen, it’s a good time to be a little smarter about how you splash around.

The bottom line: Keep your nose out of warm, still or slow-moving water — especially natural hot springs. Wear a nose clip if you’re a regular soaker, and keep an eye on any NPS visitor advisories before you head out.