The 35-year-old man from Lafayette made a distress call that his fishing boat was rapidly taking on water at about 3 p.m., officials said.
Responding crews found the man floating with a life vest near his sunken 32-foot boat, according to the Coast Guard.
A spokesperson was not immediately available to say why the boat sank.
The boat's fuel tank contained les than 5 gallons of fuel and no sheen was observed, officials said.
No serious injuries were reported.