The boy, who was South Korean and visiting family members in New Jersey, was reported missing shortly before 3 p.m. Tuesday.
Family members told police he dove into the water and did not surface.
A row of lifeguards and others joined together in a human chain, trying to cover as much ground as possible.
"We have a routine where all the parents, elbow-to-elbow, and we went across the pool," one woman said. "And we couldn't find him."
When the boy was finally found a half-hour later, he was not responding.
Emergency workers could be seen performing CPR on the boy at the shore. He was then put in an ambulance and taken to Valley Hospital, where he was pronounced dead.
The boy's name was not released.
The pool is open by membership to Ridgewood residents and taxpayers. Non-residents must be sponsored by a Ridgewood resident.
--- WEB PRODUCED BY: Bill King