Authorities say 35-year-old Edwin Barahona's body was found on shore just west of where he was last seen in the waters off Wading River early Saturday morning.
Riverhead police Detective Mike Schmidt says the Bellport man went into the water to help the boy, who was playing in the water near Creek Road while his mother took snapshots Friday night.
Jim Loscalzo helped rescue the 10-year-old boy from the waters off his beachfront home.
According to police, the boy, whom they decline to identify because of his age and his mother, also unidentified, were at the beach with her husband, the boy's stepfather, identified as Edwin Barahona, 35.
The boy was alone, chest-deep in the water, as the mother watched him from the beach, and then a strong undertow pulled the boy much farther out to sea.
"The father was fishing, and he grabbed a small swimming pool float, inflatable, and he swam out there, he got the kid on there. The float wasn't even strong enough to hold the kid's weight and I think that's when he let go," Loscalzo said.
Loscalzo and his neighbor, Bob Leech, grabbed a canoe and rushed out to help.
The rescuers not only had to pull the boy out of this water, but they had to calm him down, and in the process they lost sight of the father.
"We looked. We stayed out there for about 15 minutes, 20 minutes, rowing around, calling the guy's name, but the undertow that was out there was unbelievable," Loscalzo said.
The boy was taken to a hospital and treated for exposure.
The search continued until midnight last night.
Late Saturday morning, Barahona's body was found and pulled from the water.
(The Associated Press contributed to this report)