For Alyse Freda-Colon of Huntington and her family, the events Thursday afternoon on the beach in Robert Moses State Park were a scene out of one of her favorite movies — the summer 1975 thriller, “Jaws” — when lifeguards blew whistles and swimmers raced in panic for the shore.

“All of a sudden, people started screaming, ‘Shark!’” Freda-Colon said of her afternoon scare at the park’s Field 2, a real adventure sparked by a possible shark-sighting that began some 15 minutes after she, her husband and son arrived at the beach at 12:30 p.m.

“Everyone stood up and was running down to the water,” shesaid, adding that hundreds of barefoot spectators lined along the shore’s edge to peer out at the fin she saw moving through the water. A crew pursued in a small boat that Freda-Colon estimated would be no match for the predator, she said.

“It was just like a scene out of ‘Jaws,’” she said. “It was scary.”

But there was no sign of a shark after an hour-long search by State Parks Police, said George Gorman, state parks deputy regional director for Long Island.

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“In an hour they think they would have seen something, so we reopened the beach to swimmers,” Gorman said.

Freda-Colon said she was too upset at the time to capture the sea creature on video on her smartphone, something they didn’t have when the real Jaws debuted four decades ago.

For such an avid fan of the film, who screens it every Fourth of July at home, an hour-long investigation was too short to calm jittery nerves. Freda-Colon stayed ashore while her husband and son braved the waters once the lifeguards’ whistles signaled it was OK to get back in.

“I’ve lived here for 47 years and never heard of anything like that,” she said. “It was wild. But there was something out there.”

With Lisa Irizarry