A herd of bison are seen in the Lamar Valley of Yellowstone National Park on Aug. 3, 2016.

Matthew Brown/AP

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Matthew Brown/AP

An 83-year-old woman was seriously injured after being gored by a bison last weekend in Yellowstone National Park, the National Park Service said.

The bison was “defending its space,” and approached within a few feet of the woman on Saturday, the park said. It lifted her up about a foot off the ground.

Her current condition is unknown, and the incident is being investigated, the park said.

Bison are not usually aggressive, but can be when defending their territory. They kill humans more than any other animal in Yellowstone, and can run three times as fast as humans, the NPS said.

The National Park Service advises visitors to stay away from wild animals if they see them in places such as campsites, parking lots or trails. People should stay at least 25 yards from “bison, elk, bighorn sheep, deer, moose, and coyotes” and at least 100 yards from wolves and bears.

Several people have been gored by bison at Yellowstone in recent years, and last year a tourist from Hawaii pleaded guilty for his handling of a bison calf, which eventually led to its death.

The NPS has said bison are overpopulatedin the park. Many have had to be hunted or caught and slaughtered, while others have been transferred to Native American reservations and tribal lands.