People are being warned not to swim when lifeguards are not on duty and not to swim in areas where swimming is not permitted.
The warning comes after several people had to be rescued from the water.
A 7-year-old boy was saved after nearly drowning at Orchard Beach.
Police say the boy was not breathing when he was pulled from the water, but he was quickly revived and breathing on his own minutes later.
The boy was taken by ambulance to a nearby hospital for treatment.
Here's a look at the beach where it happened:
An NYPD officer and some local surfers rescued two people struggling in the waters off Rockaway Beach Monday night.
It was about 7:45 p.m. Monday night and beachgoers were screaming desperately for help.
Two swimmers were caught in the riptide off the shore at Beach 94th Street in The Rockaways.
The sun was setting and a frantic crowd was forming.
23-year-old Police Officer Billy Lauria happened to be there, even though he typically wouldn't.
I'm actually assigned to the 105th precinct in Queens Village," Officer Lauria said.
"Right place at right time?" Eyewitness News said.
"That's it, it was all good timing," Officer Lauria said.
Officer Lauria stripped off his belt and gun, and gave it to his sergeant, and then ran into the water to save a 25-year-old woman.
But that's when he noticed someone else who was stuck way further out.
So he enlisted help from a nearby surfer, Danny Kent, who got help from three others.
"I said, 'Everything is going to be all right, hold onto the board, we got you, everything is going to be fine,'" Kent said.
"Danny had him on his board and we switched boards, a little more sturdy to get him in," said Patsy Carroll, a surfer.
The male swimmer had gone out to save the young woman, but the crashing surf near the pylons, it's known to be treacherous there.
Anna Dyn stood on the beach in disbelief as she took pictures of the incident.
"Just froze because two helicopters flew in, they were like above my head," Dyn said.
What's clear is that had it not been for several brave heroes working together, things could've ended very differently.
"I think what makes a good surfer good, is you do the right thing without thinking about it," Kent said.
"I want to thank that gentleman," Officer Lauria said. "I didn't catch his name but I was able to shake his hand, made my job a lot easier."
Lauria had no trouble rescuing the woman, as he used to work as a swimming pool lifeguard in Hempstead.
Lifeguards are on duty at New York City beaches from 10 a.m. to 6 p.m. through Labor Day.
Two young women were pulled from the water by fellow beachgoers at Avon-by-the-Sea, near Garfield Avenue.
Both victims, ages 21 and 22, were admitted at Jersey Shore University Medical Center in Neptune in critical condition.
Sources say one of them was having difficulty swimming, and the other attempted to help her before becoming distressed herself.
Yet another female swimmer and a person with a boogie board then pulled them out of the water.
Both women were unconscious when they were rescued.
One of the good Samaritan, 32-year-old Carin Diaz, of Clifton, was treated and released from the hospital.
The Jersey Shore town will not have full-time lifeguards on duty on weekdays until their season starts June 20. For now, it is only weekends.