(A sunfish basks along Duxbury Beach. Photo courtesy of Barbara Crispi.)

A section of Duxbury Beach was temporarily shut down today when beachgoers spotted a dorsal fin 250 - 300 feet offshore. Harbormaster Don Beers immediately dispatched a boat and within minutes Officer Jake Emerson identified the fin as belonging to a sunfish and not the shark many beachgoers feared.

“It’s confirmed to be a sunfish,” said Beers, who came in on a day off to direct the search. “Nine out of ten times, shark sightings turn out to be sunfish.”

For beachgoers who saw the dorsal fin skimming the surface of their beach, especially in light of the multiple sightings of great white sharks off of Cape Cod and the July 30 attack of Christopher Myers off of Truro, it was a heart-stopping sight.

"The whole second pass saw it,” said Duxbury resident Leslie Cutler who was there with her two children, Charlie, 5, and Lila, 18 months. “Everyone ran out of the water. It was like something out of ‘Jaws.’”

Matt Keefe was also enjoying an idyllic day at the beach with his daughter, 3, when he, too, saw the dorsal fin ride the surface of the water -- a little too close for comfort.

“One of the kids saw it and I looked up,” said Keefe, who wasn’t too disturbed, noting it was shark week. “It was about 200 to 250 feet offshore and about eight to ten feet long.”

Beers said his office had received a report yesterday about a shark sighting that turned out to be nothing more than debris floating in the water. Today’s report had everyone on alert, however. He said it’s common for people to mistake a sunfish’s dorsal fin for a shark’s because of its close resemblance, its propensity to bask along the surface and size. Mola, as sunfish are more commonly known, can grow as large as 14 feet and weigh up to 5,000 pounds.

Beers said people often assume that when they swim at the beach, they swim alone. Not true.

“There are other fish out there,” said Beers. “It’s their living room and we’re playing in it with them.”