PALM BEACH, Fla. -- Visitors to Palm Beach are being advised not to go in the water because of shark sightings.

Warnings posted said hundreds of bull sharks and lemon sharks have been seen swimming along the surf, the sand bar and farther out in the Atlantic Ocean.

Lifeguards say the shark invasion happens a few times a year, often in March.

The sharks pass by every spring while migrating to their summer homes up North.

Officials first spotted the sharks Wednesday morning and said there were less by the afternoon. They're hoping there will be even fewer today.