The National Park Service (NPS) is investigating reports of a mysterious illness affecting white-water rafters who recently floated portions of the Colorado River through the Grand Canyon. According to reports, multiple rafters describe severe symptoms after separate river trips, prompting the NPS to look into potential causes and whether there is a common factor among the incidents. The reports characterize the illness as unknown, and do not identify a specific pathogen, toxin, or environmental exposure. The investigation focuses on determining what happened to the rafters and assessing whether the cases are connected. NPS officials are reported to be coordinating an inquiry into the circumstances surrounding the trips, including timing and potential exposures during rafting. At this stage, the cause and scope of the illness are not publicly established, and authorities continue to gather information from those affected as part of the ongoing probe.