TOKYO, Aug 2, 2021 (BSS/AFP) - Caeleb Dressel and Katie Ledecky ensured the United States retained their pre-eminence in the Olympic pool, but a resurgent Australia and a fast-improving British team mean they have a fight on their hands to stay on top.

The Americans came into the Games bursting with promising talent but missing a host of veteran stars, notably Michael Phelps, who loomed large at the past four Olympics.

Stalwarts Ryan Lochte, Nathan Adrian and Tony Ervin all missed out on Tokyo while Simone Manuel was unable to defend her 100m freestyle title after underperforming at the US trials.

Regan Smith shockingly fluffed the trials and did not race the 200m backstroke in Japan despite being world record holder.

Their presence was sorely missed, with their gold medal count dropping from 16 at Rio in 2016 to just 11. Altogether, they bagged 30 medals compared with 33 five years ago.

Dressel and Ledecky helped carry the team with seven gold medals between them but Ryan Murphy and Lilly King failed to defend their titles.

US women's head coach Greg Meehan put a brave face on their underperformance, insisting it was not all about winning gold.

"We've always celebrated any medal," he said. We'd love to have more golds here, like we'd like to have more medals.

"There is no disappointment, no shame from walking away from any event as a bronze or silver medallist."

Despite some high-profile failures, the swimming powerhouse did unearth exciting new talent, notably 21-year-old Robert Finke, who bagged a 800-1500m double.

There was also good news on the breaststroke front, with 17-year-old Lydia Jacoby announcing herself to the world as the new 100m champion, while teenager Emma Weyant claimed silver in the 400m medley.

Men's coach Dave Durden said the high expectations that always followed the US team were "a blessing and a curse".

"We've established a level of success in our culture that says, 'that's what we're going to do at the Olympic Games'," he said.

"It's a curse because it's like, 'you hit this many five years ago, eight years ago'. With the personnel we had this week that was a phenomenal performance."

- Liberating -

Australia, spearheaded by their women, re-established their credentials as the main challengers to the United States in the pool.

Among their 20 medals were nine gold -- their highest number at an Olympics and a huge improvement on their three titles and 10 medal-total in Rio.

Putting it into perspective, the US team won 16 gold medals to Australia's one in London in 2012 and the score was 16-3 in the pool four years later in Rio.

Seasoned campaigner Cate Campbell has witnessed the highs and lows of Australian swimming over four Olympics and said "resilience" had been their Tokyo buzzword.

"It's something we've talked about, adapting to everything thrown our way," she said. "But there has been a momentum building in this Australian swim team.

"I think everyone came into these Games 100 percent behind each and every person on the team and with the knowledge you have a team to support you no matter what the outcome -- a liberating space to be competing."

Emma McKeon won an incredible seven medals -- four gold and three bronze -- in a feat no other female swimmer has managed at a single Games.

Kaylee McKeown was another standout, clinching the backstroke double, while Ariarne Titmus dethroned Ledecky in the 200m and 400m freestyle.

Head coach Rohan Taylor attributed their success to moving the Australian trials closer to the Games, mirroring the US, but also the homely team environment.

"Obviously we have some fantastic athletes that perform when it matters," he said.

"But at the end of the day what was the really big thing for me was making sure that the (team) environment was home to them, with family."

Britain also excelled, winning eight medals, including four gold, for their best-ever haul at an Olympics.

"It's more inspiring to be part of this team than anything could ever be," said breaststroke king Adam Peaty.

"British swimming has flipped over. We deliver the goods and get the plane flying but there is a whole orchestra of people behind it."