Mystery Illness Haunts Grand Canyon Rafters

Rafters from multiple separate groups who paddled the Colorado River through the Grand Canyon are falling seriously ill — and doctors still can’t figure out why.

Story Snapshot

Multiple rafting groups from May–June 2026 trips report the same cluster of symptoms: fever, fatigue, severe muscle pain, and fluid in the lungs.
The National Park Service’s Office of Public Health has opened a formal investigation but won’t release details on the number of cases or possible causes.
One rafter spent a month sick with pneumonia and a badly infected knee requiring IV antibiotics — doctors are still stumped on what caused it.
Doctors are testing for more than ten possible diseases, including leptospirosis, Valley Fever, hantavirus, and Lyme disease — none confirmed yet.

Rafters Get Sick — Same Symptoms, Different Groups

Matthew Wappett went on a Grand Canyon rafting trip and came home with a nightmare. His knee swelled up with infection and required IV antibiotics. He developed pneumonia. For a full month, he felt like he had done a brutal workout every single day — while barely moving. “It feels like I did a hard workout every day, even though I’ve done nothing except sit on my butt,” Wappett told Paddling Magazine. Doctors are still testing him for Valley Fever, dengue fever, leptospirosis, and hantavirus.

Wappett isn’t alone. Rafter Steven King reported that four out of sixteen people in his group got sick after their trip. They had the same symptoms — fever, fatigue, severe localized muscle pain, and fluid in the lungs. King then posted about it in a Grand Canyon Rafters Facebook group. At least five other rafters reached out to say their crews had gone through the same thing after May and June 2026 trips. The pattern across separate, unconnected groups is what caught investigators’ attention.

National Park Service Opens a Formal Investigation

The National Park Service’s Office of Public Health confirmed it is investigating. The agency released a written statement saying: “At this time, the investigation is ongoing… we are not able to comment on the extent of the illnesses, potential diagnoses or other details.” The agency said it is working with public health partners, but has shared almost nothing else. That silence is frustrating for anyone trying to assess the real risk before heading into the canyon this summer.

A disease-tracking platform called BEACON Bio, run out of Boston University, created a formal report entry for “Undiagnosed febrile illnesses among Grand Canyon river rafters.” As of July 3, 2026, no diagnosis had been made public. Infectious disease specialist Dr. Britta Lassman, who co-founded the BEACON platform, is actively tracking the outbreak. She told NBC News that “the majority of disease reports end up being something identifiable — it just takes time to find out what it is.”

What Could Be Making Rafters Sick?

Doctors are working through a long list of possible causes. Leptospirosis — a bacterial disease spread through rodent urine in water — is one leading candidate given the river environment. Valley Fever, a fungal lung infection common in the Southwest, is also being tested. Other possibilities include Lyme disease, Rocky Mountain spotted fever, West Nile virus, dengue fever, and hantavirus. The wide range of theories reflects how little is confirmed so far, not how many things could be wrong.

Rafting trips in the Grand Canyon remain open during the busy summer season, with thousands of people participating each year. No warning has been issued and no trips have been suspended. That raises a fair question: if the government doesn’t know what is making people sick, should it be telling the public more? Americans deserve straight answers — not a wall of silence while an investigation drags on and tourists keep heading into the canyon. The National Park Service should be transparent about what it knows, what it’s testing, and when answers are expected.