Authorities say Oscar Menendez of Trenton and his cousins walked across a bridge at the Bull's Island Recreation Area in Hunterdon County on Saturday and decided to swim back to the New Jersey side.
Prosecutor Anthony Kearns III says the boy was about half way across the river when he began yelling for help and slipped beneath the surface.
His cousins were unable to find him and a fire department diver located the body about an hour later.
The prosecutor says the death appears accidental.
