Her Toyota sedan was spotted in the water near a town boat ramp at Barnum Avenue and West Broadway in Port Jefferson about 6:45 a.m., but police couldn't say how long it had been there.
Murray's body was removed from the car by dive teams.
Her death is not believed to be criminal in nature, but the cause has not been officially determined, said Det. Lt. Jack Fitzpatrick, head of the Suffolk County Homicide Squad.
A commercial fisherman, Gary Johnson, 56, of Blue Point, called 911 after spotting the top of the car in the water, police confirmed. He had just arrived at the dock, just west of the Port Jefferson-Bridgeport ferry terminal.
"It took a minute to realize it was a car roof," Johnson said.
Murray's family said she had been battling macular degeneration, an age-related condition that damages the center of the retina.
Her doctor told her several weeks ago that she should no longer drive because of her worsening eyesight, according to her granddaughter, Margaret Murray Posner, 38, of Long Beach.
"She never gave up driving completely, making new rules like 'I'll only drive during the day, or short distances,' " Posner said. "I'm convinced this was an accident, although I don't know if we will ever know."
Posner said her grandmother had become depressed over her medical problem, and told her last week that she planned to enroll in a program to help her deal with the condition.
Neighbors and friends described Murray as lively and generous. Her many activities including working as a volunteer at John T. Mather Memorial Hospital in Port Jefferson and helping to deliver meals provided by Three Villages Meals On Wheels, based in Stony Brook.
Eugene Carpenter, 35, and his wife, Michelle Carpenter, 34, who've lived across the street from Murray on Breton Road for seven years, said they weren't surprised she was out driving.
"She was really independent," Michelle Carpenter said. "I'd see her driving out to the store."
She could be forgetful, though, Eugene Carpenter said, noting that he would sometimes go to her house to tell her she'd left her car lights on or the trunk open.
Ronnie Kreitzer, Meals On Wheels' office manager and volunteer coordinator, said Murray had been volunteering to deliver meals, with a partner usually driving, since 1986.
"She was very giving to the community," Kreitzer said.
Murray is survived by three married children, five grandchildren and four great-grandchildren, all living on Long Island, her family said.
Funeral plans were not immediately available.
With John Valenti
An earlier version of this story incorrectly reported the year Murray began working with Meals On Wheels.