She died Thursday morning in her sleep, according to her publicist Harlan Boll.
Williams was born in Inglewood and spent her young life at the swimming pool. She had hoped to participate in the 1940 Olympics, but World War II canceled the games that year.
She was then discovered by an MGM agent, who wanted to utilize her swimming skills on the big screen. She starred in a string of popular water-filled musical spectaculars for the studio.
The extravaganzas dazzled a second generation via television and the compilation films "That's Entertainment." Williams' co-stars included the pick of the MGM contract list, including Gene Kelly, Frank Sinatra, Red Skelton, Ricardo Montalban and Howard Keel.
When hard times signaled the end of big studios and costly musicals in the mid-1950s, Williams tried non-swimming roles with little success. After her 1962 marriage to Fernando Lamas, her co-star in "Dangerous When Wet," she retired from public life.
Lamas was Williams' third husband. Before her fame she was married briefly to a medical student. In 1945 she wed Ben Gage, a radio announcer, and they had three children, Benjamin, Kimball and Susan. They divorced in 1958.
After Lamas' death in 1982, Williams regained the spotlight. Having popularized synchronized swimming with her movies, she was co-host of the event on television at the 1984 Olympic Games in Los Angeles. She issued a video teaching children how to swim and sponsored her own line of swimsuits.
The Associated Press contributed to this report.