It happened around 2:00 Tuesday afternoon in the gulf behind the Spinnaker Beach Club.
Panama City Beach Police say bystanders found 74 year old Phil Norris Long, of Richardson, Texas, face down in the water.
He was not breathing.
They pulled him to shore and began CPR.
Paramedics took long to Gulf Coast Medical Center, where he died.
Authorities are not sure if long drown, or if he suffered some other medical problem while swimming.
The Medical Examiners' Office is conducting an autopsy to determine the cause of death.