Esther Williams, a teenage swimming champion who became an enormous Hollywood star in a decade of watery MGM extravaganzas, died on Thursday in Beverly Hills, Calif. She was 91.

Her death was announced by her publicist, Harlan Boll.

From “Bathing Beauty” in 1944 to“Jupiter’s Darling” in 1955, Ms. Williams swam in Technicolor pools, lakes, lagoons and oceans, cresting onto the list of Top 10 box-office stars in 1949 and 1950.

“Esther Williams had one contribution to make to movies — her magnificent athletic body,” the film critic Pauline Kael wrote. “And for over 10 years MGM made the most of it, keeping her in clinging, wet bathing suits and hoping the audience would shiver.”

In her autobiography, “The Million Dollar Mermaid”(1999), Ms. Williams spoke of movie stardom as her “consolation prize,” won instead of the Olympic gold medal for which she had yearned. At the national championships in 1939, Ms. Williams, who was 17, won three gold medals and earned a place on the 1940 United States Olympic team. But Hitler invaded Poland, and the 1940 Olympics were canceled with the onset of World War II.

At a time when most movies cost less than $2 million, MGM built Ms. Williams a $250,000 swimming pool on Stage 30. It had underwater windows, colored fountains and hydraulic lifts, and it was usually stocked with a dozen bathing beauties. Performing in that 25-foot-deep pool, which the swimmers nicknamed Pneumonia Alley, Ms. Williams ruptured her eardrums seven times.

By 1952, the swimming sequences in Ms. Williams’s movies, which were often elaborate fantasies created by Busby Berkeley, had grown more and more extravagant. For that year’s “Million Dollar Mermaid,” she wore 50,000 gold sequins and a golden crown. The crown was made of metal, and in a swan dive into the pool from a 50-foot platform, her head snapped back when she hit the water. The impact broke her back, and she spent the next six months in a cast.

Ms. Williams once estimated that she had swum 1,250 miles for the cameras. In a bathing suit, she was a special kind of all-American girl: tall, lithe, breathtakingly attractive and unpretentious. She begged MGM for serious nonswimming roles, but the studio’s response was, in effect, “If it ain’t broke, don’t fix it.” Audiences rejected her in dramas like “The Hoodlum Saint” (1946) and “The Unguarded Moment” (1956). Her only dry-land box-office success was “Take Me Out to the Ball Game” (1949), with Ms. Williams as the owner of a baseball team whose players included Frank Sinatra and Gene Kelly (although even in that film, she was seen briefly in a swimming pool).

The men who played opposite her in a dozen lightweight comedies full of misunderstandings and mistaken identity were almost interchangeable. Johnny Johnston in “This Time for Keeps” (1947), John Carroll in “Fiesta” (1947) and Peter Lawford in “On an Island With You” (1948) were male ingénues who the studio was hoping might turn into stars. In terms of star power, she was matched on screen only by Victor Mature, with whom she had an affair when they were making “Million Dollar Mermaid,” and by MGM’s all-American boy, Van Johnson, who wooed or was wooed by her in “Thrill of a Romance”(1945), “Easy to Wed” (1946), “Easy to Love” (1953) and “Duchess of Idaho” (1950).

“Just relax,” she recalled Mr. Johnson telling her after the first few days on “Thrill of a Romance.” “It’s your naturalness that’s going to make you a star.”

Esther Jane Williams was born in Los Angeles on Aug. 8, 1921, the fifth and last child of Lou and Bula Williams. Her father was a sign painter; her maternal grandparents had come west to Utah in a Conestoga wagon after the Civil War. Unwanted by a mother who was tired of raising children, Esther was turned over to her 14-year-old sister, Maurine. The family’s chief breadwinner was her brother Stanton. A silent movie star at the age of 6, Stanton died of a twisted intestine when he was 16 and Esther was 8.

That summer she learned to swim. From the beginning, Ms. Williams wrote in her autobiography, “I sensed the water was my natural element.” She counted wet towels at the neighborhood pool to earn the nickel a day it cost to swim there. The male lifeguards taught her the butterfly, a stroke then used only by men, and, at the Amateur Athletic Union championships in 1939, the butterfly won her a gold medal in the 300-meter medley relay.

Three years earlier, 20th Century Fox had signed the Norwegian ice skater Sonja Henie, a three-time Olympic gold medalist, and turned her into a movie star in a series of skating movies, and Louis B. Mayer, who ran MGM, wanted to match Fox. The studio found Ms. Williams performing in Billy Rose’s Aquacade at the San Francisco World’s Fair. She was, as she put it, learning to “swim pretty” in tandem with Johnny Weissmuller, a former Olympic gold medalist who was already the star of MGM’s “Tarzan” films.

At first, Ms. Williams was one of two dozen MGM contract players who had, she wrote, “a look, a voice, a sparkle or a smolder.” Few lasted more than a year. To test audience reaction to her, Ms. Williams was given the role of Mickey Rooney’s love interest in an Andy Hardy movie. Half a dozen starlets — including Lana Turner, Judy Garland and Kathryn Grayson — had already been tested that way. Fan mail response to the film,“Andy Hardy’s Double Life” (1942), was unequivocal: Audiences loved the girl in the two-piece swimsuit.

At 17, Ms. Williams married Leonard Kovner, a pre-med student whom she supported by working as a stock girl at a fancy department store. It was the first of her four marriages, and he would demand $1,500 — all the money she had saved from the Aquacade — before he would agree to a divorce.

Her 13-year second marriage, to the singer Ben Gage, would bring her three children and cost her considerably more money. According to Ms. Williams, Mr. Gage frittered away $10 million of her money on alcohol, gambling and failed business ventures. He also neglected to pay taxes and left her in hock to the Internal Revenue Service for $750,000 by the time they divorced in 1959. By then, Ms. Williams wrote, “I was 37 and there was not much mileage left in my movie career.”

A decade later she married Fernando Lamas, the Argentine-born actor and director, who had helped her to swim the English Channel in “Dangerous When Wet” (1953). He was the first man who gave Ms. Williams money rather than taking it from her, but he exacted a heavy price. Her three children were not allowed to live with them or even to come to their wedding.

That marriage lasted until Mr. Lamas’s death in 1982. Six years later she married Edward Bell, a professor of French literature 10 years her junior, with whom she introduced a collection of swimwear. She also put her name on a line of successful aboveground swimming pools.

She is survived by Mr. Bell; a son, Benjamin Gage; a daughter, Susan Beardslee; three stepsons, the actor Lorenzo Lamas, Tima Alexander Bell and Anthony Bell; three grandchildren; and eight stepgrandchildren.

Asked once who her favorite leading man was, Ms. Williams offered a simple and unsurprising response: “The water.”