In front of her family, the American won the 1500-meter freestyle by 19 seconds at the World Aquatics Championships in Budapest on Tuesday. Her time of 15:31.82 was the fourth fastest in history.
The win gave the 20-year-old Ledecky her 12th career gold medal at the world championships, the most by a woman. She was also the first three-peat winner in the event. It was her third gold medal of the meet.
But Ledecky didn't have long to celebrate, as she has a chance to add to her medal haul. Back in the pool later for the 200m free, Ledecky reached Wednesday's final with the top semifinal time of 1:54.69.
"I was really just focused on the mile to begin with," Ledecky told NBC. "I just warmed up for that and then was just in a really good spot mentally, I think, after the mile, and could kind of just pretend going into the 200m like I didn't have the mile beforehand. So just approached it like any other race."
In addition to the 200m free, Ledecky is scheduled to compete in the 800m free, which she is the favorite for, and the 800m free relay, which she has a good chance to win as well. Preliminaries for the women's 800m begin Friday.
Ledecky's other gold medals at this year's worlds have come in the 400m free and the 4x100m free relay.
In addition to Ledecky's dominance, American Lilly King and Russian Yulia Efimova resumed their rivalry in the 100-meter breaststroke on Tuesday, giving flashbacks to the Rio Olympics.
A year ago in Rio after winning her semifinal heat of the 100m breaststroke, the Russian gave a No. 1 signal with her finger, which in turn offended King. King responded at the time by wagging her finger at the image of Efimova, later telling NBC, "You're shaking your finger No. 1, and you've been caught for drug cheating. I'm just not a fan." The American went on to win gold in the event.
On Monday at the world championships, Efimova gave a finger wag after winning her semifinal heat. King's response Tuesday was with another gold-medal performance, breaking the world record in the process, touching the wall in 1:04.13. Fellow American Katie Meili took silver, while Efimova settled for bronze.
Following her win Tuesday, King slapped the water in celebration and embraced Meili, telling NBC that she couldn't have asked for a better finish.
The world championships conclude on Sunday.