A Long Beach police officer who accidentally ran over a man and a woman lying on the beach Sunday night, seriously injuring both, was going less than 5 mph as he made a three-point turn, police said Monday.

Officer David Walpole hit the pair at 7:48 p.m. as he drove a pickup truck near Edwards Boulevard and the jetty, after responding to a report of after-hour swimmers in the water, police said.

Walpole, a 32-year veteran of the department, was found “not to be under the influence of any substance,” after a breath test and a check for drugs, Long Beach Police Commissioner Michael Tangney said in an interview in his office Monday.

The victims — a man, 48, and a woman, 36 — were taken to South Nassau Communities Hospital in Oceanside. Their relationship was not known, police said. Their identities were not released. The man suffered broken ribs and bruised lungs, Tangney said, and the woman injured a leg and broke a finger.

Walpole “did not notice the two [people] lying on the blanket,” Tangney said.

“He did roll over them and immediately stopped, got out of the vehicle, started to render first aid, called for additional EMS personnel.”

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Walpole was on the beach because people were swimming after lifeguards had left for the day. Swimming without lifeguards present prohibited, Tangney said. The officer, who had been on foot, got back in his truck and attempted a 3-point turn when he struck the pair, Tangney said, adding that two witnesses told police he was driving less than 5 mph.

The officer wasn’t distracted, Tangney said, adding that the high-axle 2016 Chevrolet pickup he was driving and the setting sun may have contributed to the accident.

“It was getting very close to dusk, so that could have impeded his visual ability . . . we’re still investigating the incident.”

While police investigate, Walpole is off beach patrol, Tangney said. Investigators have yet to talk to Walpole because the police union contract “precludes us from speaking to him until 24 hours after a serious incident,” Tangney said.

Ken Apple, president of the Long Beach Police Benevolent Association, said of Walpole: “He’s a very experienced police officer who’s worked the beach for many, many years. Obviously, it appears to be a very, very unfortunate accident. Our prayers go to the victims, hopefully they’re OK.”

Tangney said the department is reviewing its policies on the use of police vehicles on the beach, which typically permits ATVs during busy daytime hours when they are mostly driven in a designated lane at the rear of the beach. At night, Tangney said, officers need a fully equipped police vehicle.

“We are going to institute additional trainings to ensure that, to do our best that this never happens again,” the commissioner said.

In 2010, a Long Beach police officer hit a sunbather — an Oceanside man left with a broken spine — while driving on the beach to help rescue a swimmer. The incident was ruled an accident and the officer returned to work the next day.