"My daughter was not even 10 feet off the shore up to her waist. All of the sudden I see her panicking, and I could see something -- I couldn't tell what it was, but it was kind of flapping about," Philip Polina, the girl's father, told WABC.
The attacks happened about 4.5 miles away from each other, WNBC reports.
Officials with the National Parks Service said the bite marks on both victims are "consistent with a large fish," but there have been no sightings of a shark in the area and the incidents are not yet confirmed to be shark bites.
All public beaches on Fire Island are closed while the investigation continues.