Orange police Capt. Robert Enmon said Tommie Woodward, 28, suffered severe trauma to a limb when he was attacked early Friday morning at the private marina, which is along a bayou extending from the Sabine River near the Louisiana line.
Reports suggest the man shouted "f*** these alligators" before he jumped into the water.
"He said blank the alligators and thereupon jumped into the water," Orange County Justice of the Peace Rodney Price told KFDM.
Price said the 28-year old was almost immediately attacked and another young girl jumped in after him.
"Next thing I know this girl is screaming an alligators got him, an alligator's got him and I grab a flashlight trying to zoom it over the water, trying to find him," Wright said.
"The next thing I know, I don't even know how long it was, I saw his body floating face down and then he's up there for a couple seconds and then he gets dragged back down and pulled off."
Orange County sheriff's deputies and a Texas game warden found his body nearby about two hours later.
Police said Woodward, who lived near the marina in Orange, was swimming with a woman, but Justice of the Peace Rodney Price told KFDM-TV that she only jumped from a dock after he screamed for help. The woman was not hurt.
The owners of the marina recently had spotted a large alligator on a few occasions, and put up a sign warning people to stay out of the water, Enmon said. They estimated that animal was longer than 11 feet.
The reptile could have been startled early Friday or was possibly protecting its habitat, Enmon said.
"You've got to remember that alligators are a predatory species, they are territorial, and they will take advantage of an opportunity," he said.
Authorities are not hunting the alligator but a private effort may be launched to capture it, he said.
This is the first fatal encounter with an alligator that Enmon can recall in his 25 years in law enforcement.