HELENA, Mont. — A film producer from Massachusetts accidentally drowned this week while scuba diving in a Montana lake during a video shoot for a prospective U.S. Senate candidate, authorities said Thursday.

The possible candidate, John Mues, tried to help 40-year-old Jesse Hubbell before Hubbell went under Monday in a lake east of Helena, Lewis and Clark County Sheriff Leo Dutton said.

The men were filming a video for Mues, a Navy veteran with diving experience who is considering running against Republican U.S. Sen. Steve Daines in next year's election.

They were in water at least 60 feet deep, while two other members of the film crew and Mues' wife were in a nearby boat, sheriff's Capt. Kevin Wright said.

Divers searched Canyon Ferry Lake for two days before finding Hubbell's body Wednesday.

"We have ruled it as an accident, and the cause was drowning," Dutton said. "We're still looking into what were the causal factors."

The possibilities include an equipment malfunction and hypothermia, and investigators were awaiting toxicology reports, the sheriff said.

The water in Canyon Ferry Lake is between 60 and 64 degrees (16 and 18 degrees Celsius), Montana Fish, Wildlife and Parks spokesman Greg Lemon said.

Water that cold can lower a person's body temperature and risk hypothermia, but both men were wearing wetsuits and had been in the water for about 10 minutes when the accident happened, Wright said.

Hubbell had some diving experience, but authorities did not know how much.

Hubbell was a freelance producer for 17 years from the Boston area who worked on films, documentaries and political and commercial content, according to his LinkedIn profile.

A former co-worker, Dan Casey, said Hubbell specialized in lighting, was a sound engineer and was a good cameraman with a great sense of humor. Casey said he was stunned by his death.

"He was an asset in any crew," Casey said. "If Jesse was on the crew, you knew you were going to have a good day."

A close friend and former colleague, Jimmy Jay Frieden of Boston Digital Productions, said Hubbell was recently married and had been doing a lot of work on political videos recently.

Frieden did not know what kind of diving experience Hubbell had, calling him adventurous but very safety conscious.

"There's nobody I know who was more aware of what was going on on set, who always had your back and was super smart," Frieden said.

Mues did not return a call, email or text seeking comment.

He had to be treated at a hospital Monday after trying to help Hubbell, but Wright did not know the nature of Mues' injuries and he was released the same day.

Mues has not filed to run against Daines, but he had a campaign website that was taken down after Monday's accident. The website described him as a fourth-generation Montana resident, a Navy veteran, an engineer and a teacher.

He previously told the Washington, D.C., political publication The Hill that he was planning to announce his Senate candidacy soon. It's not immediately clear how the accident affects his plans.