Duxbury Beach was temporarily closed Friday after an unconfirmed shark sighting.
"All of a sudden the lifeguards just yelled 'Everybody out of the water, out of the water everybody!' And everybody immediately got out of the water, no hesitation," one woman who was at the beach Friday said.
The news was communicated via a tweet from Duxbury Police Beach Operations shortly before 2 p.m. The beach, which was packed with parents and kids, was reopened within about an hour.
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Although the apparent danger was gone, frayed nerves were left behind.
"It is a little scary. I didn't get into the water for the day," one beachgoer said.
"I didn't see anything at all, but you never know what's creeping around out there, so I will just stay in the sun," another said.
Several great white sharks have already been observed off Cape Cod and other areas of New England over the past week.
The Atlantic White Shark Conservancy spotted over a half dozen great whites during a research trip Monday in Cape Cod Bay. That same day, the Chatham harbormaster reported seeing a 13-foot great white eating a seal near Monomoy Island.
Last week, police in Manchester-by-the-Sea on the North Shore of Massachusetts reported that a large shark was seen near House Island. Swimmers were cautioned but not ordered out of the water.
Sharks typically return to the Massachusetts area in June.
Last year, two people were attacked by sharks on Cape Cod, including Massachusetts' first fatal attack since 1936. The first attack occurred on Aug. 15 at Longnook Beach in Truro. The victim, a New York man, survived but was badly injured. The second attack on Sept. 15 at Newcomb Hollow Beach in Wellfleet claimed the life of 26-year-old Arthur Medici of Revere.
Ever since, towns on the Cape have been wrestling with a variety of possible solutions for the shark crisis, including building ocean barriers and reducing the seal population.