The report from the office of the Chief Medical Examiner said 24-year-old Sgt. Shane Scott Pease of Decatur, Mich., drowned after he fell and hit his head.
It also said Pease had a high blood-alcohol level of .18 percent. The legal limit in North Carolina is .08 percent.
A jogger discovered Pease on Nov. 19 with his head submerged in Bolin Creek. Chapel Hill police have said they think his death was an accident.
Pease was a paratrooper with the 82nd Airborne.
His father spoke with ABC11 days after Pease was discovered. Jimmy Pease said he had no idea how his son came to be in the area where he was found.
"It don't make no sense. If they was going hunting like my son said, where's the gun? He wouldn't be hunting in an area like this in the first place," said the elder Pease.
Shane Pease deployed to Iraq twice. His most recent tour ended in November 2009.
Pease's father said his son loved being part of the military.
"He loved nature. He loved defending his country," he said. "Me and him had done plans of riding, a whole year of riding our bikes through Montana, Seattle, California, just follow the coast."
His father said he was just days from completing his service with the military.