Ledecky, Katinka Hosszu, Adam Peaty, and Caeleb Dressel will have their work cut out at the star-studded FINA swim champs in Gwangju, South Korea.
Rivalries will be renewed and records likely broken as the world's best swimmers go head-to-head at the 18th FINA World Championships in Gwangju, Korea, where swimming events take place July 21-28.
The event will mark one year to go until Tokyo 2020 and, with Olympic qualification berths up for grabs, expect fast times at the state-of-the-art Nambu University Municipal Aquatics Center.
Can anyone catch freestyle favourite Katie Ledecky?
All eyes will be on the five-time Olympic champion as she bids to win four individual gold medals in Gwangju, eclipsing her treble at the bi-annual event in 2017.
Olympic Channel will be on-site in Korea, bringing swimming fans the latest news, exclusive interviews and more. Read on for our essential guide to everything you need to know about the event, with the 2019 FINA World Championships schedule here.
Ledecky has already stated her intention to complete in the 200m, 400m, 800m, and 1500m freestyle events at Tokyo 2020.
However, Gwangju will be the first time she attempts the quadruple at a world championships, and it will be fascinating to see if she can sustain her best form over such a punishing schedule.
Perhaps the biggest threat to the American's lofty ambitions comes in the form of fellow Stanford swimmer Taylor Ruck.
The Canadian teenager caused the shock of the 2018 Pan Pacific Championships when she beat Ledecky in the 200m freestyle final, setting a new national record in the process.
The threats don't end there either!
Beijing 2008 Olympic 200m freestyle champion, and world champion Federica Pellegrini may choose to defend her title in Gwangju, having pipped the American to the 2017 worlds title.
That's despite it being possibly her weakest event, as the current Olympic champion Ledecky is still the hot favourite over 200m, and will be keen to avenge both defeats.
There will be high expectations in the men's events for Caeleb Dressel.
The American was named Male Swimmer of the Meet in 2017 with seven victories (equaling Michael Phelps' record), including three individual golds in the 100m butterfly, 50m freestyle, and 100m freestyle.
Dressel will be favourite for all three events again, plus the 50m butterfly, which he has added to his schedule for Gwangju.
In 2018, the 22 year old's star shone even brighter after he became a full-time professional, sealing six golds and three silvers at the short course world championships in Hangzhou, China.
Keep an eye in particular on bandana-wearing Dressel's 100m freestyle progress at Gwangju 2019, where he will likely go head-to-head with Olympic champions Sun Yang and Chad le Clos in what would be one of the most explosive races of the meet.
While Le Clos will have to settle for the underdog tag in that event, the South African may fair better in his favoured 200m butterfly.
The 27 year old pipped Phelps to Olympic gold over the distance at London 2012.
"With all due respect to my competitors, the only medal I'm going for is gold and I believe that I will win," Le Clos told Olympic Channel at his Doha training base.
Katinka Hosszu's form since Rio 2016 has been inconsistent, but there is no denying that on her day she is still the world's best.
The triple Olympic gold medallist was one of the stars at the 2017 FINA World Championships, with two individual medley golds, and silver in the 100m backstroke.
However Hosszu decided to take a career break early in 2018 due to personal reasons, before returning in style to claim four more individual golds at the FINA Short Course World Championships.
Rivals of the 'Iron Lady' should be warned: Her red-hot form in the recent Mare Nostrum series, including the world's fastest 400m individual medley time this year, suggests the charismatic Hungarian has fully rediscovered her best form.
"You know it might be fair to say that I am better than before," Hosszu told Olympic Channel at her training base in Budapest.
"I actually have been able to swim a couple of season times that I have never done before which is even for me, it's a great surprise.
"I think that's the ultimate goal to be the fastest ever."
With such a strong line up of swimmers packed into one event, expect world records to be broken.
At the head of the pack chasing new world best figures is Rio 2016 Olympic 100m breaststroke champion Adam Peaty.
To be more exact, the Brit is actually hoping to break his own world records in the 50m (25.95 secs) and 100m (57.10 secs) breaststroke.
"Going for 56 seconds (in the 100m breaststroke), that would be almost two seconds faster than anyone else, and that would be very special but I don’t get sucked up in it, I don’t let it control me, I just go out there and do what I do," said Peaty, who set new 100m breaststroke world record figures in Rio.
"When I have fun and when I’m focused, and passionate, and a little bit angry, I use that emotion to propel myself forward," Peaty told Olympic Channel.
"I’ve been undefeated at the 100m breaststroke now for five years, how do you find that extra motivation? I’ve been very driven since I started the sport and I don’t intend to change now. I’m all about moving forward and not taking the past into account."
The 2019 FINA World Championships coincides with a golden age in women's swimming.
While there will be several races littered with Olympic gold medallists, perhaps the most eagerly anticipated is the women's 100m freestyle.
In the FINA Champions Series 2019, Swedish Olympic gold medallist Sarah Sjostrom has ruled the waves with three wins from three events, and is odds on to win in Gwangju.
However with fellow Olympic champions Pernille Blume, Penny Oleksiak, Federica Pellegrini, Simone Manuel, Ranomi Kromowidjojo, and Cate Campbell likely to be challenging for this title, an epic showdown awaits in Korea.
Sjostrom is having an unbelievable year, having also remained unbeaten in the Champions Series over both the 50m and 100m butterfly events.
However, her biggest challenge is now to produce her best performances when it matters most, something that she has sometimes failed to do in the past big finals.
The FINA World Championships will count as a Tokyo 2020 Olympic qualifying event for individual athletes that meet the required times for their event.
The Games in Japan will see a maximum of 16 teams qualify per relay event, with a one-team maximum allocation for each National Olympic Committee.
The 12 highest-placed nations per relay event at the 2019 World Aquatics Championships will qualify for the Olympics in Japan based upon the final standings.
23 Jul - 8 Aug 2021
Tokyo 2020 | Olympic Games
Although the FINA World Aquatics Championships in Gwangju take place July 12-28, the swimming events take place in the final week only: From 21-28 July.
Don't forget to follow the Olympic Channel's daily live blog from the World Championships in Gwangju.