An autopsy found no signs of drug or alcohol in Hill's body, although more tests are planned and will take two weeks to complete, said Orleans Parish coroner Dr. Frank Minyard.
Minyard said Hill might have suffered a mild concussion when he fell off the water craft.
The former LSU star and a female friend had ventured onto the lake near the south shore. Investigators said neither was wearing a life vest. Authorities said they ended up in an area of swirling currents near where a shipping canal runs into the lake.
While the woman survived by clinging to a pylon until she was rescued, the 24-year-old Hill, who friends described as a good swimmer, drifted away and disappeared. Searchers pulled his body from the water on Monday afternoon.
Loved ones including Hill's fiancee, Inell Benn, and friends, including Patriots teammate Randall Gay, had waited anxiously along the shoreline during the search and consoled one another when authorities told them Hill was found dead.
"Right now's a terrible time," Benn said. "I don't know what to feel right now."
Gay, who also played with Hill at LSU, had planned to spend the holiday weekend in Baton Rouge, but drove to New Orleans on Monday to monitor the search.
"Knowing that I have to go back to work and go look at his locker this week, it's tough," Gay said.
Hill's body was discovered by searchers about a quarter of a mile from where he fell into the water, Capt. Brian Clark of the Louisiana Wildlife and Fisheries Department said.
"I lost a brother, man," said Patriots defensive lineman Jarvis Green, a fellow Louisiana native and former LSU player. "He was a funny guy. ... He'd just sit there and talk to you, say some funny things off his head that'd make you laugh. He was good to be around."
The Coast Guard was called Sunday night, Petty Officer Tom Atkeson said. The search began immediately, using boats and helicopters.
By the time the body was found, the Coast Guard, Wildlife and Fisheries, the New Orleans Police Department and Jefferson Parish Sheriff's Department were involved, Clark said.
Hill played on LSU's national championship team and was a second-round draft pick by New England in 2004. He had yet to start for the Patriots, playing in 13 games in his NFL career.
"We have suffered a stunning and tragic loss," Patriots coach Bill Belichick said in a written statement. "Marquise will be remembered as a thoughtful and caring young man who established himself as one of the year-round daily fixtures of our team. I send my deepest condolences to the Hill family."
The rescued woman, whose identity was not immediately available, was sent to Tulane Medical Center, where she told authorities Hill had tried to keep her calm as the two were drifting away from each other.
"It's so important to have a life jacket and a signaling device," Atkeson said. "One keeps you afloat and the other helps us find you."
Hill's agent, Albert Elias, said the player spent much of his time since Hurricane Katrina helping rebuild the homes of family members including his mother, Sherry, and the mother of his 2-year-old son.
"From what I hear, he's done a lot to help with things after Katrina, and I know he had a great passion for the city of New Orleans," said former LSU quarterback Matt Mauck, who was Hill's teammate at LSU. "Off field he was a really kind person, kind of like a gentle giant. And not only for LSU, but for New England and everyone who got a chance to meet him throughout his life, everyone has to be extremely saddened and disappointed to hear the news."
After heading to the NFL, Hill continued to do much of his offseason training at LSU's Baton Rouge campus, about 80 miles up the Mississippi River from New Orleans. He was known and admired by current Tigers players, university athletics spokesman Michael Bonnette said.
"His presence meant a lot for some of the younger guys. He gave them someone to look up to and he was always there for them," Bonnette said. "Here's a 6-foot-6, 300-pound guy, as intimidating as can be, and yet every time you approached him he always welcomed you with a big old smile.
"In between the lines, he had his game-face on, but outside the lines, in the community or in the weight room, he was always smiling and having a good time."