Four years after a spate of shark attacks prompted a media frenzy, is another "summer of the shark" about to break over us? A week ago last Saturday, a shark killed a 14-year-old girl off the coast of Destin, Fla.--the first fatal attack in the state since 2001. Two days later and 90 miles away, another shark tore into a 16-year-old boy, who survived but lost his leg. While "two shark attacks in three days is unusual," says John Tyminski of Mote Marine Laboratory, "there's no reason to believe it's anything more than coincidence." Shark attacks have risen over the years--hitting a high of 52 in the United States, and 79 worldwide, in 2000--but experts attribute the increase to larger numbers of beachgoers, not a change in the animal's behavior. In Florida, which ranks highest in attacks, this year's tally is consistent with the state's recent average of roughly 30 attacks per year.

Most shark attacks result from cases of mistaken identity. "What appears to them to be a prey item"--like a fish or sea turtle--"turns out to be a human being," says Greg Skomal of the Massachusetts Division of Marine Fisheries. Poor visibility caused by murky water or breaking surf can add to the confusion. During summer, when sharks venture closer to shore in search of food and the water is packed with vacationers, the likelihood of such encounters increases. Bull sharks--believed to be the culprits in the two recent Florida attacks--are especially pugnacious and often found in shallow water. To guard against mishaps, Erich Ritter of the Shark Research Institute argues that swimmers should be confined to areas patrolled by lifeguards and barred from approaching piers, where fishermen using live bait may attract sharks. Other tips from experts: avoid swimming at dawn and dusk when sharks feed, stay away from steep underwater slopes where the animals sometimes hang out and don't wear shiny jewelry that can be mistaken for fish scales. Shark attacks "are extremely rare," says John Carlson of the National Marine Fisheries Service. But never forget "it is the ocean. It's not your swimming pool."