Three visitors and two concessions employees at Yellowstone National Park have tested positive for COVID-19, the park reported on Tuesday.
"Some of these visitor cases had symptoms prior to entering the park," Superintendent Cam Sholly said in a statement. "If you have symptoms as your visit is approaching, do the responsible thing and don't come to the park. You end up putting our employees, health care providers, and other visitors at risk."
National parks are taking precautions against the virus, but it's not easy, in part because visitors are flocking to outdoor destinations they perceive as safe.
Yellowstone reported visitation in late June that topped numbers over the same period in 2019.
Every national park is taking a different tack during the pandemic. Rocky Mountain National Park in Colorado, for example, is only allowing 60% of its visitor capacity, and people have to buy a pass to enter during a specific time window.
"I think that parks are doing their best to comply with the CDC guidelines," said Phil Francis with the Coalition to Protect America's National Parks.
But he stresses that visitors need to as well, and urges them to do a better job of practicing social distancing.
As for masks, the National Park Service doesn't require them, though in Yellowstone, the park's primary concessionaire does, effectively making masks mandatory in all public indoor facilities.
This story has been updated to clarify that masks are required indoors in Yellowstone National Park.
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.