Thousands of sharks swim by Fla. shore

PALM BEACH, Fla. (NBC/WPTV) - Beaches in the Palm Beach area are closed to swimmers after thousands of sharks have been spotted swimming along South Florida shores.

Tens of thousands of sharks have been spotted from Boca Raton to Jupiter since the start of the month.

Marine biologists say the sharks are moving north after migrating south for the winter.

In the helicopter video, hundreds of sharks swimming along Palm Beach.

On Tuesday, lifeguards spotted a shiver of spinner sharks moving through Midtown Beach and put up red flags, indicating swimmers could not go in the water. While the sharks are interesting to watch, they are dangerous to swimmers.

Doctors at a Florida hospital say they treat at least five- to six shark bite victims a year. And while the injuries are usually minor, even a small shark bite can put a victim at risk for infection.