Katie Ledecky showed she was at the peak of her powers at the age of 26, winning the women's 800-meter freestyle on Saturday to retain her title and surpass Michael Phelps with a record 16th individual gold at the world championships.

Ledecky led from start to finish and touched the wall in 8:08.87, four seconds outside of her 2016 world record, to become the first swimmer to win a single worlds event six times -- doing so consecutively as well.

It was Ledecky's second gold at these worlds, along with winning the 1,500 free earlier this week, giving her 21 worlds golds overall. She also took silver in the 400 freestyle.

But that winning time -- the seventh quickest she ever swum -- wasn't quite good enough in her favorite event.

"I'm just always trying to think of new ways to improve. I mean, I've already got everything turning in my head right now. I kind of wanted to be better than I was tonight," Ledecky said, twirling her right hand beside her right ear, trying to stir up ideas. "I'm pretty tough on myself, but I think I have found the balance of being tough on myself but also having that grace."

She went 4.44 seconds faster than silver medalist Li Bingjie of China (8:13.31), with Australia's Ariarne Titmus (8:13.59) collecting bronze.

"It's fun to leave a meet with your favorite event, and I just wanted to leave it all in the pool," Ledecky said.

Sarah Sjoestroem cruised to her fifth straight world title in the women's 50 butterfly before breaking the world record in the 50 freestyle in the semifinals.

Sjoestroem, 29, finished the opening event in 24.77 seconds to hold off China's Zhang Yufei, who was 0.28 seconds behind. Gretchen Walsh of the United States took bronze in 25.46.

"That was amazing, I'm very proud of this gold, which is the fifth one. It's amazing," said Sjoestroem, who tied Phelps with 20 individual medals at the world championships. "I feel like I enjoy it more than ever at the moment."

Sjoestroem then produced a superb effort of 23.61 seconds in the freestyle to better her own mark of 23.67 seconds, which she had set in the 2017 worlds in Budapest.

Another world record fell when the Australian mixed 4x100m freestyle relay team of Jack Cartwright, Kyle Chalmers, Shayna Jack and Mollie O'Callaghan lowered their world record in the final race of the evening as they finished in 3:18.83. The U.S. took the silver in 3:20.82, with Britain getting the bronze in 3:21.68.

Australia's Olympic and world champion Kaylee McKeown sealed a first-ever backstroke treble for a woman at worlds as she roared to the 200 backstroke title after prevailing in the 50 and 100 earlier in the week.

McKeown, who holds the 200 backstroke world record, finished in 2:03.85 to beat American Regan Smith, who finished more than a second behind in 2:04.94 despite leading early in the race. China's Peng Xuwei took bronze in 2:06.74.

"That means a lot. I didn't think I'd be able to do that tonight, especially after a long week," McKeown said. "That's the best thing about sport, you have to focus on your own race, and that is exactly what I did tonight."

French swimmer Maxime Grousset took gold in the 100 butterfly in 50.14 seconds to finish ahead of Canada's Josh Liendo and American Dara Rose. It was France's fourth gold of the meet, with Leon Marchand grabbing the other three.

Australia's Cameron McEvoy won the men's 50 freestyle gold in 21.06 seconds, outclassing silver medalist Jack Alexy of the U.S. by 0.51 seconds. British swimmer Benjamin Proud took bronze.

The Americans lead the overall table with 31 medals (4 gold, 16 silver), Australia has 20, including 13 golds, and China 13.

Reuters and The Associated Press contributed to this report.