Videos have been popping up on social media of schools of brown, kite-like rays gracefully moving through the water around fascinated swimmers at the Jersey shore.
Thomas Grothues, associate research professor at Rutgers University's department of of marine and coastal sciences, said they're mostly Cownose rays.
"Their numbers are peaking now, so it's a seasonal phenomenon, so it's not unusual (that) they're here. They're eating clams in the shallow water," Grothues said.
The rays propel themselves by flapping their wing-like pectoral fins, which, when the pointy tips clear the water, may have some swimmers thinking they're sharing the surf with something else altogether.
They have serrated barbs at the base of their whip-like tails which they use to defend themselves against predators.
Grothues said they're not likely to trouble you unless you trouble them.
"If you do step on them, they're likely to get you in the foot or the calf. It happens very very infrequently," he explained.
Sharing the water with them may become more common. Grothues said the rays' numbers are increasing because the their main predators, hammerhead sharks, are in major decline.