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KAZAN, RUSSIA - AUGUST 03: Katie Ledecky of the United States reacts after setting a new world record of 15:27.71 in the Women's 1500m Freestyle Heats on day ten of the 16th FINA World Championships at the Kazan Arena on August 3, 2015 in Kazan, Russia. (Photo by Adam Pretty/Getty Images)

KAZAN, RUSSIA - AUGUST 03:  Katie Ledecky of the United States reacts after setting a new world record of 15:27.71 in the Women's 1500m Freestyle Heats on day ten of the 16th FINA World Championships at the Kazan Arena on August 3, 2015 in Kazan, Russia.  (Photo by Adam Pretty/Getty Images)