The women went to the shore where one called 911, drawing a multiagency response from local law enforcement; Fish, Wildlife and Parks; and Life Flight, a medical air transit service in the Rocky Mountain and Pacific Northwest regions.

The women, who were not identified, were treated at a hospital in Bozeman. The most severely injured woman suffered wounds on her face and arms, Jefferson County Undersheriff James Everett told the Associated Press. The other women suffered injuries to their arms.

“It’s just not something you run into very often,” Everett said. “Bears do it, moose too and occasionally a deer, but otters? That’s not normal.”

Further updates on the women’s condition were not available.

Staff with Montana’s Fish, Wildlife and Parks have since posted signs at fishing sites around the area and alerts about otter activity. “No further management action is planned at this time,” the department said.

Though attacks by river otters are uncommon, reports of unusual or surprising interactions with animals like otters and orcas have grabbed headlines this summer.

A 5-year-old sea otter in Santa Cruz — known as Otter 841 — continues to evade capture (and thrill locals) after weeks of approaching kayakers and biting surfboards. Wildlife experts have been unable to determine whether Otter 841’s aggressive behavior was prompted by something like hormonal changes or becoming accustomed to being fed by humans.

Other high-profile encounters with wildlife in recent months have been more terrifying. An Arizona woman survived after she was gored by a bison in Yellowstone National Park — the first incident of its kind this year. It was unclear how close the woman was to the bison before the attack.

Meanwhile, reports of orcas sinking boats and damaging sea crafts have ballooned, with more than 500 known incidents in the past several years. Researchers say the behavior is probably orcas, particularly juveniles, trying to have fun.

Otters, too, are known for their highly social behavior, often playing in groups and sometimes hunting in pairs. Montana Fish, Wildlife and Parks said otters rarely attack, but they can become protective at close distances, particularly of their young. Otters typically breed in the springtime, with their pups swimming with them in the summer.

The last known attack by a river otter came almost exactly two years ago in Montana amid similar circumstances when a 12-year-old boy floating in an inner tube on the Big Hole River was attacked by an approaching otter and sustained minor injuries.