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The woman was visiting the park Wednesday when she approached a bison in the Old Faithful Upper Geyser Basin and was knocked to the ground, park officials said in a news release.
Park medics responded and evaluated the woman, who chose not to go to a hospital, the release said. Officials did not name the woman and no details on her injuries were given.
The park instructs visitors to stay at least 25 yards away from all large animals, the release said. It is investigating the incident, which marked the first time a bison injured a park visitor this year.
Earlier this month, when the park was still closed, a woman who illegally entered the grounds suffered burns after accidentally falling into a thermal feature near Old Faithful Geyser.
On Monday, Yellowstone National Park entered its first phase of reopening, weeks after its March 24 closure due to the coronavirus outbreak.
The limited Phase 1 reopening, of a three-phase plan, encourages guests to “follow all CDC and local health guidance by practicing good hygiene and social distancing,” officials said in a news release announcing the plan. The park recommends wearing a face covering when social distancing is not possible.
Wyoming, where most of Yellowstone is located, lifted out-of-state quarantine orders before requesting that park entrances in the state reopen. However, the park’s West, North and Northeast entrances in Montana and Idaho remain closed due to 14-day quarantine mandates for out-of-state visitors.
The park is working closely with states and counties to reopen the remaining three entrances as soon as possible.
Fox News' Alexandra Deabler contributed to this report.