Triple champion O'Callaghan produced one last searing freestyle leg to conclude the program on Saturday but the Australian women's 4x100m medley team just missed out on victory behind the US.

Earlier at the Duna Arena, Meg Harris produced a brilliant finish in the 50m freestyle, clocking 24.38 seconds to snatch a tie for third and grab Australia's last individual medal of the week.

Then after a podium near-miss from the men's fourth-placed 4x100m medley outfit, the equivalent women's quartet of Kaylee McKeown, Jenna Strauch, Brianna Throssell and O'Callaghan took silver in three minutes 54.25 seconds.

It was the team's 17th medal of the week as a new-look Dolphins team, without some of Australia's biggest Olympic names, finished with six golds, nine silver and two bronze.

They finished third on the medal table behind Italy (seven golds) and the Americans, who were in a league of their own, collecting 17 golds among a record-breaking collection of 45 medals in all.

"It's an awesome team to be a part of, it always is no matter what our medal tally is," said McKeown.

"To get up off the back of an Olympics last year, it's incredibly hard and a real testament to us as Aussies and our drive and determination to build on that depth within this team."

O'Callaghan was the undoubted star of Australia's campaign in Hungary, the 18-year-old Queenslander ending up with three golds - in the 100m free, women's 4x100m free and the mixed 4x100m free - and three silvers in the 200m free, women's 4x200m free and now the women's medley relay.

"It's definitely about the girls, not so much about me," said O'Callaghan, deflecting praise.

"It's a team thing at the end of the day. I'm extremely proud of the girls, they should be very proud of themselves."

Still, there was perhaps a tinge of disappointment that they couldn't quite end up with a seventh gold after qualifying as fastest from the heats.

World 100m record holder McKeown, who'd taken the individual 200m title in Budapest, was expected to give the Olympic champions a flying start on the opening backstroke leg but finished only third in 58.77, way off her world mark of 57.45.

Strauch, silver medallist in the 200m breaststroke, and butterfly swimmer Throssell, with three relay medals to her name already in Budapest, fought to get the Dolphins back in it.

But O'Callaghan was still left a second down as she tackled the Americans' freestyle anchor Claire Curzan.

As in her individual 100m final, the 18-year-old again produced a turbo-charged finish over the last 25 metres, clocking the best anchor leg of 52.30, but was left 0.47 behind as the American foursome of Regan Smith, Lilly King, Torri Huske and Curzan enjoyed toppling the Tokyo winners.

In the 50m free, Albury's Harris, a member of the Aussies' Olympic-winning 4x100m free quartet, earned her first individual global medal in dramatic fashion.

In a hectic last-ditch splash for the wall, the 20-year-old couldn't be split from fellow bronze medallist American Erika Brown.

They finished level behind Poland's silver medallist Katarzyna Wasick (24.18) and the great Swede Sarah Sjostrom, who took an astonishing 19th individual world medal - just one behind all-time record holder Michael Phelps.

In his first-ever international final, Isaac Cooper was seventh in the 50m backstroke in 24.76, while Dolphins rookie Jenna Forrester finished in the same position in the 400m medley final.

Australian Associated Press