An "exceedingly rare" series of two shark attacks off the Florida coast left multiple people injured last week, but experts say beachgoers shouldn't be alarmed.

The latest two attacks on two beaches in the state left three people injured in the span of just one and a half hours on Friday. The first victim, a 45-year-old woman, was swimming past the first sandbar of a beach in Watersound with her husband when the shark attacked. She had part of her left arm amputated and suffered "significant trauma" to her midsection. Watersound is on the Gulf coast around 120 miles west of Tallahassee.

Two 15 and 17-year-old girls were attacked less than 4 miles up the coast in Fort Walton as they swam in waist-deep water with a group of friends. One girl sustained "significant" injuries to her hand and leg, while the other took minor flesh wounds to her foot.

A third attack occurred the same day. A 25-year-old woman was taken to a trauma hospital in serious condition after a shark attack near the Hawaiian island of Oahu.

"It's rare, exceedingly rare, to have three victims in one day," South Walton Fire District Fire Chief Ryan Crawford said at a news conference on Friday.

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Experts say attacks rise with more people in the water

Shark attacks and fatalities rose last year. But experts say recent numbers are not out of the ordinary.

Researchers at the International Shark Attack File, part of the University of Florida's Florida Program for Shark Research, confirmed 69 unprovoked bites worldwide, up from the 5-year average of 63 attacks, with 52% occurring in the U.S., and 16 in the state of Florida. The attacks left 10 people dead, five more than the year before.

So far this year, shark bites have decreased, said Gavin Naylor, the head of the research program and manager of the file. "This year has been very, very low, but it's ticking up now," he said.

Naylor said when warm weather brings more people into the water, the chance of attacks increases.

Bait fish, which sharks feed on in the Florida area, also swim close to shore, upping the risk of a shark encounter, he said. "You have humans swimming in the water and sharks feeding on their normal food source and it's right in where the people are, and accidents happen," Naylor said.

Local officials still saw the back-to-back attacks as an anomaly.

Mackenzie McClintock, public information officer for the South Walton Fire District, called last week's incidents "very rare." The last death from a shark attack in the jurisdiction was in 2005, nearly a decade ago, she said.

"This is not something that we have ever experienced before," she added. She said 20 to 30 personnel responded to the attacks, including some medical responders that arrived in helicopters.

The two victims with severe injuries have a "fighting chance," Walton County Sheriff Michael Adkinson said at a news conference on Friday evening.

In a post on fundraising site Caring Bridge, a mother of one of the teenage girls injured in the attack, said she and a friend rushed to the beach when she heard the reports of a shark to find her daughter on the ground "lifeless her eyes closed mouth white and pale."

"The wound on her leg or all that was left of her leg was something out of a movie," she wrote.

A spokesperson for the family declined to comment further to USA TODAY.

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Bull sharks, common to Florida, likely behind attack

McClintock said officials don't want to speculate on what kind of shark was behind the attack. But Naylor said a bull shark was almost certainly behind it. The species is one of two, along with the tiger shark, that swim close to the Florida shoreline, he said.

He said local deputies told him after the attacks that drone footage captured bull sharks swimming close to the shore. Around 60 to 70 sharks could swim near the coast every day, he said.

"It's not unusual. And they mind their own business," he said.

Better water quality could also contribute to shark attacks, according to shark researchers at the university. For instance, improved water quality around New York could have factored into the first reported shark attack in the New York City area in more than half a century last year.

The August attack, at Far Rockaway Beach in Queens, left a 65-year-old woman seriously injured. New York authorities said several shark bites were also reported earlier in the summer.

In the wake of the two attacks, fire officials warned beachgoers not to "underestimate the open water and any of the marine life that could be present," according to a Facebook post from the Fire District on Sunday. Lifeguards on Dune Allen Beach continued to fly purple flags, indicating the presence of dangerous marine life. Authorities also closed the beach for less than 24 hours.

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at [email protected]. Follow her on X @CybeleMO.