Gary Smith of Wantagh said he was at Jones Beach State Park at about 6:15 a.m. Tuesday when he spotted Pablo Perez, 47, wandering near the boardwalk, the New York Post reported Wednesday.
"He was easily 6-3 and over 300 pounds," Smith said. "I asked him where he came from, and he said he'd been out on a raft for the last three days. He told me he was fishing and that his raft was tied to another boat and became detached and he drifted out to sea."
Police said they cut a .25-caliber semiautomatic, which was loaded and unlicensed, out of Perez's wetsuit. He was arrested for criminal possession of a weapon and taken to a hospital to receive treatment for dehydration and exhaustion.
Investigators found a 9-foot raft nearby where Perez was first spotted, police said.
State Park Police Chief Richard O'Donnell said officers are still investigating the "very unusual incident."