Authorities are using boats to patrol the ocean and warn swimmers of shark activity this weekend along the coast of Florida's Gulf, where three people were injured in separate shark attacks on Friday.

The attacks off the shores of Florida's Panhandle prompted authorities to temporarily close several beaches to swimmers on Friday. The beaches reopened on Saturday with flags raised to warn of high risks.

In Walton County, the sheriff's office, fire department, and state wildlife agency were working together to patrol the waters by boat and the beach by vehicle, according to a Saturday update from South Walton Fire District. The attacks occurred on Friday in Walton County.

Please swim cautiously today, respect the Gulf, stay hydrated, and look after your loved ones."

Red and purple flags were used on Saturday to warn swimmers of dangers.

The Bay County Sheriff’s Office posted on social media on Saturday: "Purple flags indicate the presence of dangerous marine life, and single red flags indicate extremely hazardous conditions."

The Bay County Sheriff’s Office noted that small fish are schooling near the shore at this time of year, which may be a contributing factor to the attacks.

The Walton County Sheriff’s Office reported that the first attack occurred Friday afternoon when a woman was bitten by a shark near Watersound Beach. Ryan Crawford, chief of South Walton Fire, stated at a press conference that the woman sustained serious injuries to her torso and arm, and part of her arm was amputated, as she was airlifted to a trauma center.

According to the sheriff's office, less than two hours later, firefighters responded to another beach about four miles (6.4 kilometers) east of the first attack "after multiple reports of a teenager being bitten by a shark."

South Walton Fire District stated that two teenage girls were in the water up to their waists with a group of friends when they were attacked.

Fire officials said in an update: "When rescuers and deputies arrived on the scene, they found one female with serious injuries to the upper part of her leg and one of her hands." She was airlifted to a trauma center. The other teenager sustained what officials described as minor injuries to one of her feet.

Crawford said, "It is very unusual for two incidents like this to occur on the same day."

Michael Atkinson, mayor of Walton County, noted that the timing of the attacks - in the mid-afternoon - was also unusual. He pointed out that law enforcement officials often warn people about shark activity early in the morning and at dusk, which are typical feeding times.

Officials also reported on Friday that in Hawaii, a woman was seriously injured in what appeared to be a shark attack in waters off Oahu.

According to experts, shark attacks are rare.

There were 69 unprovoked bites worldwide last year, with 10 of them fatal, according to the International Shark Attack File at the University of Florida. This was above the recent average of six fatalities annually.