(CNN) -- Mitchell Guist, a star of the reality TV show "Swamp People," died of "natural causes," a local sheriff in Louisiana said.
Assumption Parish Sheriff Mike Waguespack released the preliminary autopsy conclusion Wednesday, although he said final results will not be available for another four or five weeks.
Guist, 47, was working to build a houseboat when he appeared to have a seizure and fell backwards in his boat, said Assumption Parish Sheriff Mike Waguespack.
He was with another person on the Intercoastal Waterway, about 75 miles from New Orleans, at the time of his collapse.
That person, who did not want to be identified, got Guist back to a boat landing, performed CPR and called his wife, who in turn called 911, said the sheriff.
Guist was transferred to the Teche Regional Medical Center in Morgan City, where he was pronounced dead Monday.
Daniel Wiltz, with the St. Martin Parish coroner's office, declined to comment on the autopsy except to say that it was pending.
"Right now, we're thinking about him almost every minute," said Brian Catalina, executive producer of "Swamp People." "We've lost a really important part of our family and a treasured friend."
"Swamp People" is the popular History Channel TV series that chronicles the lives of alligator hunters.
Now in its third season, the series is set in Louisiana's Atchafalaya Swamp, and focuses on Cajun alligator hunters during the 30-day hunting season that the History Channel notes is "crucial to their survival."
Guist appeared on the show alongside his brother, Glenn Guist.
"The two were inseparable. These guys were born in the same house that they both still lived in, up until yesterday. They were two peas in a pod for sure. Neither had ever married. They were just as brothers as you could be," said Catalina on Tuesday.
Soon after news of Guist's death broke, tributes began pouring in on the brothers' official fan club Facebook page.
"RIP Mitchell you were one hell of a swamp man and inspired people like me. Prayers go out to Glenn and the Guist family. May his legacy live on," read one.
"May the king of the bayou welcome you home," read another.
CNN's Joe Sutton contributed to this report.