|Katie Ledecky of the U.S. celebrates after setting a new world record to win the women's 1500m freestyle final during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Michael Dalder|
The 16-year-old, who also took the 400 metres freestyle title on Sunday, touched in a time of 15 minutes 36.53 seconds to destroy the previous best of 15:42.54 set by compatriot Kate Ziegler in 2007.
Lotte Friis of Denmark led for much of the race at the hilltop Palau Sant Jordi, with Ledecky lurking on her shoulder, but could not match the American's late burst and finished with silver in 15:38.88, also inside Ziegler's mark.
Lauren Boyle of New Zealand was third in 15:44.71 ahead of Spain's Mireia Belmonte Garcia in 15:58.83.
"It was really tough, my hardest race ever," Ledecky told reporters.
"I knew we were going pretty fast and I figured that whoever came out on top was probably going to get the world record.
"I had to be careful not to push it too early or push it too late and just touch the wall first."
(Reporting by Iain Rogers; Editing by John Mehaffey)