The victim, identified as Michael Lee Gilbert, 56, was pronounced dead at the scene.
A boater spotted what appeared to be a person floating in the waters off Manhattan Beach Pier around 2:20 p.m. Thursday.
Baywatch officials launched a search but rescue efforts were scaled back as the sun began to set.
Gilbert's body was subsequently spotted by a Coast Guard helicopter floating in nearby King Harbor at 5 p.m, according to Charlie Kissel of the Los Angeles County Fire Department Lifeguard division.
Gilbert, a known transient, was wearing clothing, but no life vest or other flotation device.
Anyone with information about this incident is encouraged to contact the Los Angeles County Sheriff's Department's Homicide Bureau at (323) 890-5500.