The incident took place around 3:30 p.m., when the unidentified male was swimming with a group of other teens.
Emergency responders pulled the teen from the water and immediately began CPR, Dan Keefe, deputy public information officer said.
Unfortunately, the individual was not able to be resuscitated, he added.
The official cause of death will be determined by the Rockland County medical examiner. Authorities have not released his identity or where he is from.
Located in both Rockland and Orange counties, Harriman State Park is the second largest state park in New York.
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