US National Parks Service Investigates Mysterious Cluster Of Illnesses In Visitors To The Grand Canyon

Back at the beginning of June, Matthew Wappett, executive director of the Center for Persons with Disabilities at Utah State University, took a boat out on the Colorado River, which passes through the Grand Canyon. 

"Three days after returning home, I was in the ER with a swollen knee, fever, and bone-crushing aches in my joints. The doctors thought it was a staph infection in my knee and started me on IV antibiotics and oral antibiotics," Wappett explained in a Facebook post, "although they never got a positive staph culture, even after arthrocentesis and blood cultures."

Despite the medical attention and course of antibiotics, Wappett continued to experience discomfort, describing it to Paddling Magazine as if he had had the flu for the past month.

"Although the massive course of antibiotics took down the swelling in my knee, which ended up being diagnosed as cellulitis, I have continued to have fevers, severe bone and joint aches, and I was just diagnosed with pneumonia this week," he added, posting in the Grand Canyon Private Boaters group. "Essentially, I've felt like crap ever since returning home... and no, it's not the post-trip blues."

Looking at the private boaters group, Wappett discovered that he wasn't alone, and at least five other rafters claimed to have had similar symptoms following trips to the Canyon. The Biothreats Emergence, Analysis and Communications Network (BEACON) now lists two incidents of groups falling ill after rafting their way down the river.

"In the first group, four of 16 trip participants (25%) developed symptoms after returning from a 07–22 Jun 2026 trip; symptoms were first compared and reported among group members on 01 Jul 2026 and included fever, chills, fatigue, weakness, and muscle soreness progressing to severe muscle pains," they explain. "One person was reported to briefly have lost consciousness in their doctor's office and was subsequently hospitalized. Some individuals had 'fluid in their lungs' and one individual reportedly developed a raised rash/bruising on their shin."

The National Parks Service is now investigating the illnesses following these reports but thus far has not disclosed any conclusions, if any have yet been reached.

“At this time, the investigation is ongoing, and we are not able to comment on the extent of the illnesses, potential diagnoses or other details while the investigation is underway," it told Paddling Magazine. "We will share additional information with the public as it becomes available."

While the illness remains unidentified, there are a number of possibilities, including "valley fever," a fungal infection that is acquired by inhaling microscopic spores from the soil, which can cause pneumonia-like symptoms and can be misdiagnosed as pneumonia. Another possibility is a waterborne pathogen, such as Leptospira spp, which can cause similar symptoms to those experienced and is known to affect whitewater rafters. On the brighter side, BEACON suggests that the bubonic plague is unlikely given the symptoms described, though Yersinia pestis, the plague bacterium, is endemic to the area.

"The spatiotemporal clustering of illnesses across two independent trip groups using the same river corridor over a five-week window (May–June 2026) strongly suggests a shared environmental or vector-borne exposure source," BEACON continues. "The absence of gastrointestinal symptoms and the predominance of musculoskeletal, pulmonary, and febrile presentations focuses the differential toward zoonotic, vector-borne, or inhalation-acquired pathogens endemic to the canyon environment."

Until the National Parks Service investigation concludes, we won't know exactly what the nature of this illness is, though anyone who experiences similar symptoms after a trip to the Grand Canyon is encouraged to contact the NPS Office of Public Health.