The St. Tammany Parish Coroner's office has identified the swimmer as Ferrell Smith, 25.
Crews found Smith's body near a marina in the Oak Harbor area.
The man was reported missing after 4 p.m. on Friday.
Witnesses said he put down a backpack and jumped in but didn't resurface.
St. Tammany Parish sheriff's deputies searched the 20-foot-deep body of water and using sonar to try to locate the missing man.
Officers discovered the body around 5:45 p.m.
"From what we understand the subject may have had a backpack with him that he left on the dock, and then that's when he went into the water swimming for unknown reasons. We do believe we may know who this person is but obviously, we can't confirm that," Capt. Daniel Seuzeneau said. "You just don't know with these waters and what to expect."
Dr. Charles Preston will conduct an autopsy Monday, but the presumptive cause of death is drowning.
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