Several people reporting seeing a shark off South Beach in Edgartown on Saturday, prompting swimmers to evacuate the water and giving at least one person a scary close encounter.

Eva Bradford, 22, of Westport, Me., was swimming about 30 feet from shore at about 7 p.m. when she heard her two cousins screaming. At first she couldn’t make out what they were shouting about, but soon realized they were yelling “shark.”

“And I looked over and I saw it about 10 feet from me. I could see its dorsal fin and its tail fin . . . I think it was swimming around me,” she told the Gazette yesterday.

Ms. Bradford, who works as a lifeguard at a beach in Maine, said her first reaction was one of wonder, which quickly changed to fear. “We don’t see many sharks in Maine. At first I thought wow, that’s pretty cool, then after a few seconds I thought: this is bad. I better get out of here,” she said.

As she made her way to shore, two men who also spotted the fin started running toward her, yelling at her to get out of the water. Meanwhile, all swimmers headed for the shore. Ms. Bradford was able to swim to safety; later she talked to someone who spotted seals in the area just prior to the scare, which may have attracted the shark.

Shark sightings always cause a stir on the Vineyard, in part because the movie Jaws was filmed here some 35 years ago. Last summer a series of shark sightings drew national media attention. One sighting turned out to be a hoax.

Some type of large fish was spotted off South Beach on Saturday. Although town officials are taking it seriously, they have not closed beaches.

Edgartown personnel director Marilyn Wortman, who oversees the town lifeguards, speculated the fish spotted Saturday may have been a sunfish sunning. Lifeguards at the beach are under no special instructions to look out for sharks, she said, although scanning the water is part of their normal job description.“That’s what they’re there for.”

As for the fish spotted on Saturday, Ms. Bradford said it was hard to identify.

“It was pretty big . . . it was dark gray. It looked like a shark,” she said.