Swimmers and holidaymakers fled Florida beaches after thousands of sharks appeared too close to shore.
Coastlines along south Florida were shut to bathers because of the risk of attacks.
It was estimated that up to 15,000 blacktip and spinner sharks were as close as 200 yards to beaches.
But the predatory big fish were not there to feast on human flesh. The sudden appearance of the animals was a natural phenomenon: they were migrating northwards.
A few lone sharks swam up to the shoreline and holidaymakers photographed their close encounters - from a safe distance.
Double red flags were hoisted in Palm Beach, Boca Raton, Boynton Beach and Singer Island.
Swimmer Elizabeth Horowitz said: "People really need to heed these warnings becase thank God it's a public beach and they have these warnings.
"Sharks are to be reckoned with."
Although the two species are timid and rarely if ever attack people, coastguards were concerned that the sheer number of the sharks may have sparked panic.
Shark season began this year around a month later than normal, possibly due to the warmer winter.