People reported hearing gunshots in the area just after 2 p.m.
Lifeguards rescued him from the water and learned he was a 75-year-old man reported missing from Las Vegas.
“It is unacceptable that we have 16- and 17-year-olds who are being introduced to the gang lifestyle,” LBPD Chief Robert Luna said.
Police arrested 42-year-old Hery Martinez-Paredez, at his home in Long Beach on suspicion of indecent exposure. He is being held in the Long Beach jail on a $200,000 bail.
The man was found severely beaten at 1 a.m. on Jan. 5 in an alley near 68th Street and Paramount Boulevard.
The case of a decades-old Long Beach gang killing ended in a mistrial Friday when jurors deadlocked 8-4 in favor of finding the defendant guilty.
In total, detectives confiscated the seven gambling machines, one gun and over $1,700 in cash, police said.
Police were called to the scene at Third Street and Magnolia Avenue at about 11:16 a.m.
The suspects are male, police said, and the incident is being investigated as possibly gang related.
Police do not yet know the motive for the shooting but said the suspect is a woman.