The shiver, mostly blacktip and spinner sharks, is making its way up the East Coast and keeping swimmers away.
Researchers at Florida Atlantic University say they have counted more than 15,000 sharks, most less than 200 yards from shore.
"We don't have a sandbar." lifeguard Craig Pollock, a Palm Beach lifeguard supervisor told ABC News. "A lot of times when we have a sandbar the sharks stay off of the shore a little further."
Many beaches are flying a double red flag Thursday, warning beachgoers to stay out of the water.
According to the International Shark Attack File at the Florida Museum of Natural History, there were 80 unprovoked shark attacks worldwide in 2012, 26 of which were in Florida.