American Missy Franklin, 17, collected her third gold medal -- and fourth medal overall -- of the London Olympics on Friday when she set a world record in the 200 backstroke.

Franklin clocked 2 minutes, 4.06 seconds, 0.75 quicker than the mark set by Kirsty Coventry of Zimbabwe at the 2009 world championships in Rome.

Fellow American Katie Ledecky -- who, at 15, is the youngest member of the U.S. swim team -- won the 800-meter freestyle. Ledecky narrowly missed a world record in the grueling race, falling off pace on the last lap and finishing in 8 minutes, 14.63 seconds.

Franklin, who will be a senior at Regis Jesuit (Aurora, Colo.), also won gold in the women's 100-meter backstroke and and 4x200 freestyle relay, and bronze in the women's 4x100 freestyle relay. She is scheduled to swim in one more event, the 4x100 medley relay, on Saturday.

Ledecky, who will be a sophomore at Stone Ridge School of the Sacred Heart (Bethesda, Md.) this fall, says freestyle isn't even her best event. "When I was younger, butterfly may have been my better stroke," she said earlier this spring.