Nauset Beach in Cape Cod had to be closed to swimmers on Monday - after a lifeguard spotted a 13ft great white shark in the water.
Orleans Harbourmaster Dawson Farber said a dorsal fin was spotted about 150 yards off the beach towards the southern end of its protected swimming area, reports Cape Cod Online.
Farber added that, as per protocol, swimmers were asked to get out of the water for an hour.
If no further sightings occur after an hour, swimmers are allowed back in the water.
The sighting has sparked a surge in 'shark-spotting tourists', said Nauset Beach clam shack owner John Ohman.
He told the Boston Globe: "There is a great curiosity that you might be able to see a great beast of the deep. I'm anticipating that there will be a surge of people interested in looking for a great white shark."
And one beachgoer, Irena Rietveld, told the paper: "It's why I wanted to come here. I've always thought that people think that sharks are mean and vicious, but they're really not."
Dawson Farber added: "I'm anticipating that it will be a draw for people.
"We recognize the fact that there are sharks in the area, and we really feel the need to raise the education level of the people who come down here so they're reminded that there is an inherent risk any time you go in the Atlantic Ocean."
Beachgoers described seeing a "very large black dorsel fin" break the surface near the man, who then struggled to shore with bites on his legs, according to Cape Cod Online.
And, also in July 2012, one man's first experience in a kayak turned out to be more dramatic than he expected when a great white shark appeared in the water right behind him at Nauset Beach, Cape Cod.
Walter Szulc Jr was paddling his canoe when he spotted a shark's fin in the water, seven feet behind him.
The area is famous for being the spot where Steven Spielberg shot his hit shark film, Jaws.
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Kayaker spots 14ft great white shark swimming right behind him