State parks spokesperson George Gorman said park police and staff were "continuously monitoring the waterways" after a lifeguard in the water felt something biting his calf. The lifeguard suffered a one-inch laceration, which could be a shark bite.
Drones were launched to search for sharks but none were seen.
An EMT treated the lifeguard on the beach. He then went to a hospital and is expected to be OK, officials said.
Lifeguards reported seeing a fin in the water around 11 a.m., officials said.
"Our lifeguards are scanning the waters, we have the ability of drones to scan the waters, we're on the watch, have been on the watch," Gorman said, adding that state park police were also monitoring the water.
Marine experts say that schools of bunker fish often draw sharks closer to the shore.