NJ Fish and Wildlife are looking into the claims of the sightings in the Navesink River in Rumson.
Authorities sent a note to residents to be cautious in the area around Navesink Avenue, even though no shark sightings have been confirmed.
Police Chief Scott Paterson said in the past they've had nurse sharks in the water and a few years ago even a beluga whale.
He said the shallow, warm water of the river attracts a variety of sea life.
Paterson said it's possible the shark sightings may have actually been cownose rays which are often attracted to the area.
When the rays turn, their wings often stick out of the water and look similar to a shark fin.
On Thursday, a sea turtle who was entangled in a fishing trap line and was being circled by sharks off New Jersey was rescued by a Coast Guard cutter.
Sea turtle entangled in line, circled by sharks rescued
Sea turtle entangled in line, circled by sharks rescued
On Long Island, several shark sightings have prompted beach closures this past month.
Tracking efforts underway as nearly 20 sharks spotted near Long Island in 2 weeks
With 20 sharks spotted in 2 weeks, tracking efforts underway on Long Island
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