Olympic Channel were on site in Korea as Adam Peaty and Katinka Hosszu claimed swimming titles, but Sarah Sjostrom was beaten.
Olympic Channel are on site at the FINA World Championships in Gwangju, South Korea.
The high diving events also began, while in the water polo, the women's semi-final lineups were decided.
You can re-live all of Monday's action with our blog below (newest updates first). Come back for daily live blogs throughout the Championships.
Alternatively, you can catch up with what happened on Sunday 21 July here.
12 - 28 Jul 2019
FINA World Championships - Gwangju
All times below are Korean Standard Time (UTC+9 hours).
That's it for another day here in Gwangju!
Thank you as always for joining us on our daily blog.
We have five more finals in the pool tomorrow evening, while the medallists will be decided in the women's high diving (it's pretty wild).
Here's a gallery of today's best photos. You wouldn't catch us jumping off from that height!
So, both Adam Peaty and Katinka Hosszu have won their first finals in Gwangju.
Our man Andrew Binner spoke to both of them before all three headed out to Korea.
China's Sun Yang, who won the 400m freestyle title yesterday and finished second in tonight's 200m free semis, spoke to media in Chinese in the mixed zone afterwards.
"I hope he will recover as soon as possible, return to the pool and contribute his strength to Asian swimming," Sun said.
"We have been competing for lots of years, I really don’t treat him as a rival, the relationship between us is like friends.
"He has a health problem, and as an athlete, I can understand his feeling right now.
"Both of us have won everything, I wish him a quick recovery and return to competition as soon as possible."
At least two swimmers struggled earlier this morning with the backstroke starting wedge (see 5:37 pm and 6:48 pm).
A decision had been made not to use the start wedge in semis and finals, before that was later overturned and swimmers were allowed to use it, albeit in a fixed setting for everyone.
Rio 2016 silver medallist in the women's 100 back Kathleen Baker, who qualified fourth for tomorrow's final, spoke about its importance after her race.
"The wedge is so important for backstrokers, not flipping and not having issues like that… Taking that stress away with the wedge is amazing.
"Having to hear we might not be able to use it was very anxiety-producing for every backstroker here, just asking every coach on staff, ‘Can you change this? Can you change that, is it an option?’
"I’m lucky it’s there; I haven’t had an issue with it. I know the boys have struggled. I’m doing fine and I’m happy the wedge is there."
Katinka Hosszu had a difficult 2018 which was beset by personal issues.
Reflecting after retaining her 200m IM world title, the Hungarian said: "From the outside it might seem like just another gold medal, but listen, for me it’s really special to be here and being able to win this title. I’m looking forward to a lot of work for next year. I’ve learned a lot from last year.
"Coming into this World Champs and just really deciding to prepare for Tokyo, I decided to have fun with swimming. I actually got a bit carried away yesterday because I felt the world record is so close and after the semis I was like, ‘Oh, I’m not fast enough’, but I went home and thought about it and after last year I wouldn’t have thought that I’d have been here.
"I need to enjoy, this is a journey, and I still have one year to go to Tokyo. I like it when I still have something to get so I’m happy that I didn’t break the world record and I still have something next year."
On withdrawing from the 100m backstroke, the 'Iron Lady' explained that was decided last night due to the scheduling of her events.
"We were going to see whether I would finish or not as there was another Hungarian in the event. Something didn’t work out with the timing with the 100 back in the morning.
"I wasn’t going to swim in the semis anyway, but we kept the option open to swim. We decided last night I wasn’t going to swim."
It came as a surprise to Caeleb Dressel to learn that he's the first American to win the 50m butterfly at the World Championships.
"I had no idea. I’m glad to be a part of it, I don’t think it’s something I was too worried about. The 50 stroke in the US isn’t particularly of importance, we’re starting to do it more, it’s not really a thing. At least we’ve got one guy in there and I’m glad it could be me.
"It shakes it up, it’s just a fun event. The 50 fly for me brings something different, it’s good old-fashioned racing in an event that’s just at Worlds. It doesn’t have that same pressure on it."
The winner ahead of Sjostrom, Canada's Maggie MacNeil, explains what went through her head at the end of the race.
"I could see Sarah out of the corner of my eye, our arms are kind of equal, so I’m like ‘I’m just going to put my head down and get to the wall as fast as I can’.
"I’m very surprised, but very happy with how it’s been going this year. I’m going to keep working hard and hopefully make the team next year, that’s the goal going forward."
Sarah Sjostrom was beaten in a surprise result in the women's 100m fly, and in the mixed zone afterwards joked about the attention she was receiving.
"There’s so many cameras! I feel like I’ve never had this many microphones when I’ve won before, it’s only when I come second!"
The Swede was in an upbeat mood, and admitted she couldn't have won today.
"I feel like I couldn’t really do better than that today. Obviously I would be happier with a gold medal.
"I felt already in the semis and prelims that I can’t really hold the last 50 together, I’m quite exhausted in the end.
"I’m actually surprised I did a 56.22 with that hard finish. I wish I could complain, but I actually had a pretty good race.
"It’s just the back-end speed, but maybe it’s just age or something. I don’t know."
Adam Peaty, who clocked 57.14 to win the 100m breaststroke final, says he's "a little bit" disappointed at not breaking his world record again today.
"I'm still learning a lot about the event, and learning a lot about myself, and it's still a 57.1 which is almost a second and a half faster than the rest of them, so very happy.
"With that constant expectation that I put on myself, it's a little bit disappointing to me, but I think that will fuel me for next year because I know how bad I want to go below 56, even faster now and I know exactly how to do it.
"I obviously ran out of opportunities here, so I'll just enjoy it, enjoy the moment.
"To go 57, 56, 57, it's out of this world really and no-one else has even got near that on a one-time.
"I think for the Olympics next year, I have got a lot of learning to do, a lot of pacing to do. Instead of going a little bit crazy in the semi-final, maybe I need to hold back the guns and let the emotions out in that final."
Here it is. A head-to-head swim-off. Belgium's Fanny Lecluyse and Italian Arianna Castiglioni face off for a spot in the women's 100m breaststroke final.
It's close, but Castiglioni is pulling clear in the back 50 and it's the Italian who'll make it through! 1:06.39, a new personal best.
World and Olympic champion Katinka Hosszu is behind at 100m! But only just, by 0.08 seconds.
She's pulled away on the third leg, and here comes the freestyle - she's well clear - victory for the Hungarian swimmer in 2:07.53!
Silver to Ye Shiwen of China; Sydney Pickrem of Canada claims bronze.
Australia's Clyde Lewis won that first men's 200m freestyle semi-final from Lane 1!
He beat Sun Yang to the wall.
"It's big for me, but I've learned to calm down, I've still got a job to do tomorrow night when it really counts," he notes in the mixed zone.
Here comes the second semi-final, it's a very tight finish at the wall and Lithuania's Danas Rapsys has won it. The Kazan 2015 world champion James Guy was sixth, but it's so close and he might be out of the semis.
Lewis, Sun, Rapsys, Duncan Scott, Katsuhiro Matsumoto, Dominik Kozma, Martin Malyutin, and Filippo Megli make it through - so no spot for USA's Townley Haas either.
FINA has sent a warning letter to Swimming Australia and Mack Horton over Horton's medal ceremony protest against Sun Yang yesterday.
A FINA statement reads:
The FINA Executive met today in Gwangju (KOR) to analyse the situation related with the men’s 400m free victory ceremony and has decided to send a warning letter to Swimming Australia Ltd and to athlete Mack Horton (AUS).
While FINA respects the principle of freedom of speech, it has to be conducted in the right context.
As in all major sports organisations, our athletes and their entourages are aware of their responsibilities to respect FINA regulations and not use FINA events to make personal statements or gestures.
The matter over which Mack Horton was allegedly protesting is currently under review by CAS and therefore it is not appropriate for FINA to prejudice this hearing by commenting further.
The three medallists in the women's 100m fly, MacNeil, Sjostrom, and McKeon, have just stood on the top step of the podium with words written on their palms:
It's Canadian Kylie Masse, in the absence of Olympic champion Katinka Hosszu in this event here in Gwangju, who's topped the timesheets in the semis for the women's 100m backstroke.
It's a time of 58.50, and she qualifies ahead of Minna Atherton of Australia 0.1 second behind and her teammate Taylor Ruck.
Rio silver medallist and world record holder Kathleen Baker qualifies in fourth. The other finalists are Kaylee McKeown (Australia), Olivia Smoliga (USA), Daria Vaskina (Russia), and Natsumi Sakai (Japan).
Can Caeleb Dressel win his second gold of this Championships?
The men's 50m fly is up.
Defending champ Ben Proud is in lane one. The world champ Andriy Govorov in this race too.
It's tight! Caeleb Dressel does it, lowering his Championship record from yesterday to 22.35. It's the USA's first gold medal in this event in Worlds history.
Silver to Oleg Kostin of Russia; bronze to the 39-year-old Nicholas Santos of Brazil.
Russia's Yulia Efimova (1:05.56) and USA's Olympic and defending world champ Lilly King (1:05.66) lead the list of qualifiers for tomorrow's final in the women's 100m breaststroke.
Japan's Reona Aoki, Italy's Martina Carraro, South Africa's Tatjana Schoenmaker, Britain's Molly Renshaw, and China's Yu Jinyao make up the rest of the finalists.
Belgium's Fanny Lecluyse and Italian Arianna Castiglioni will have a swim-off.
Both Xu Jiayu and USA's Ryan Murphy were under the 100m back world record mark for a while there, but they just eased off that pace at the end.
A new Championship record 52.17 for the Chinese.
Through to the final are Xu, Evgeny Rylov, Murphy, Matt Grevers, Mitch Larkin, Ryosuke irie, Guilherme Guido, and Robert Glinta.
They are indeed allowing start wedges here, unlike what was thought earlier.
But they're all fixed in one position for all the swimmers.
The men's 100m back semis come first.
Nine of the pool's ten lanes are in use, from lanes 0 to 8.
Sarah Sjostrom, the defending world and Olympic champion in the 100m butterfly, is in this final.
She's about half a body length ahead down the back straight but is being caught!
Could this be a surprise defeat?
It is! Margaret MacNeil of Canada takes the world title from Sjostrom!
55.83, a new Americas record. Sjostrom clocked 56.22; Australia's Emma McKeon won bronze in 56.61.
He's way ahead of everyone else! Under the world record split at 50 metres, he's going to win gold!
Will this be a new World Record?
No! He just faded slightly at the end, 57.14. It's still Peaty's third world title in this event.
It's a British one-two as James Wilby finishes second, in 58.46. China's Yan Zibei wins bronze in 58.63, a new Asian record.
Here we go with the day's first final! The Men's 100m breaststroke.
The pool is ready, the spectators are ready, the swimmers are ready, and so are the Japanese TV broadcasters!
Swimming finals start in 10 minutes.
Olympic champion and world record holder Katinka Hosszu goes in the Women's 200m individual medley final tonight.
Oh wow! A very late chance for Italy to tie it up with six seconds left in the fourth quarter but the shot is saved by the Hungarian keeper!
What a big play! Hungary have taken a time-out. They just need to play smart in these last two seconds and it's over!
Hungary have beaten Italy by the smallest of margins, 7–6, and will face Spain in the semi-finals.
Five minutes left in this quarter-final and there's no separating the two teams. Italy and Hungary are tied at six.
In case you missed it, Adam Peaty became the first breaststroker to go under 57 seconds over 100m yesterday.
After the problems this morning during heats (see 5:37 pm), a decision has been taken not to use start wedges tonight.
For the first time at a World Championships, video replay is in use in water polo in the form of Video Assistant Referees (VAR), just as in football and various other sports.
The VAR officials can make use of screens to rule on goals, as well as violent play.
It was one of a number of law changes in the sport brought in just this year.
We're underway between Italy and Hungary.
All over in the third women's water polo quarter-final.
Spain have beaten Netherlands 12–8 to make the semi-finals, where they will play the winner of the last quarter-final between Italy and Hungary.
Normally the best 16 swimmers in morning heats qualify for semi-finals in the pool.
But in tonight's Men's 100m backstroke semis, there will be 18 swimmers – two heats of nine.
Sabbioni struggled with his start wedge twice (once in his original heat and also in his first attempted re-swim), while Carter also appealed for a re-swim. Carter broke his national record in his re-swim.
They displaced Hungary's Richard Bohus and Italian Thomas Ceccon out of the top 16 respectively, but FINA have granted both swimmers places in tonight's semis.
We're not out of the first quarter, Spain lead 6–0, and the Dutch have made a goalkeeping change.
And they're finally on the board! 6–1 now.
In the third women's water polo quarter-final, Spain have gone into an early 4–0 lead against Netherlands in the first quarter.
The Dutch look pretty stunned, and have called an early timeout.
At the conclusion of the first two round of the men's competition, USA's Steve Lo Bue is in top spot with 218.40 points.
Mexico are also in the hunt for medals in the form of second-placed Jonathan Paredes, while Czech Republic's Michal Navratil is third.
It's amazing to see how close the high diving athletes are, each one embracing the other before competition. Perhaps this is not such a surprise given how dangerous their sport could be.
The women's water polo Olympic and World champions are through to the semi-finals, dispatching Greece 15-5.
Divers plunge in to a deep pool from 20m (women) or 27m (men) and can reach 85km/h!
Mexico's Adriana Jimenez finished top of rounds 1 and 2 in the women's high diving competition with 148.2 points, with Team GB's Jessica MacAulay in second and Genevieve Bradley of the United States in third.
Every diver gets four dives of varying difficulty ratings, over two sessions.
Mexico is synonymous with high diving, and they will be extra pleased about this one.
The quarter-finals are beginning imminently and here are the match-ups:
2:00 pm - USA v Greece (USA are Olympic champions and on a run of 50 consecutive wins - the longest streak in Olympic era of women’s water polo.)
3:30 pm - Russia v Australia
5:00 pm - Spain v Netherlands
6:30 pm - Italy v Hungary
Fans seeking refreshment after the morning's water polo and swimming events are flocking to the food village, which is sitting pretty in the sunshine today.
Following Katie Ledecky's shock 400m Freestyle yesterday, the American's World Championships are back on track with a comfortable victory in the 1500m Heats.
Ledecky wasn't even using her legs and finished in 15:48:90, the fastest time in qualifying.
That brings to and end another excellent morning session of swimming.
Recently-crowned 400m Free world champion Sun Yang wins the most closely-fought heat this morning.
Lining up against 100m Free Olympic champion Kyle Chalmers, the Chinese showed no hangover from his medal-winning exploits yesterday to edge the Australian by 0.14 of a second.
But an amazing swim in the final heat sees Britain's James Guy pip both men going into this evening's semi-final with 1:46:18!
The vertigo-inducing high diving competition is about to start at Chosun University.
The women drop in from 20m, and the men from 27m.
No surprises here. Women's 100m Breaststroke Olympic champion and world record holder Lilly King dominates the heats in Gwangju with 1:06:31.
After a sluggish start for highly-rated Yuliya Efimova, the Russian clinches her heat and second overall.
The semi-finals take place this evening.
Going into these championships, many saw Ryan Murphy as the man to beat in the Men's 100m Backstroke.
Keen to silence the doubters, Chinese world champion Jiayu Xu has just set a blisteringly quick 52.85 seconds to qualify for the semi-finals in top spot.
American Murphy can only manage second place in his heat, and the ninth-quickest time to qualify for the semis.
Buenos Aires 2018 Youth Olympic Games star Kliment Kolesnikov also qualifies, finishing fourth in his heat.
Canadian Olympic bronze medallist Kylie Massie sets the fastest Women's 100m backstroke qualifying time in 58.91 seconds.
In her first race in four months (due to a rib injury), world record holder Kathleen Baker wins her heat, but only with the fourth-fastest time.
Massie's compatriot Taylor Ruck finishes second in her heat behind Australian Kaylee McKeown.
As top 16 finishers, all qualify for this evening's semi-final.
The referees are behind the blocks, the athletes are in the waiting room, the Women's 100m Backstroke heats are about to begin!
Team USA's Kathleen Baker and Canadian Kylie Massie are the favourites.
08:00 - 18:30 Water polo: Women's quarter-finals
10:00 - 12:45* Swimming preliminary rounds
Women's 100m Backstroke
Men's 100m Backstroke
Women's 100m Breaststroke
Men's 200m Freestyle
Women's 1500m Freestyle
20:00 - 22:15 Swimming
Men's 100m Breaststroke final – Adam Peaty (GB) is aiming to break his own world record from semi-finals.
Women's 200m IM final – Katinka Hosszu (HUN) is the only woman to have won the this event three times, meaning victory today would enhance her own record.
Men's 100m Backstroke semi-final
Women's 100m Breaststroke semi-final
Men's 50m Butterfly final – Caleb Dressel (USA) could win his ninth world gold medal and also secure the United States its first world title in this event.
Women's 100m Backstroke semi-final
Men's 200m Freestyle semi-final
Women's 100m Butterfly final – Sarah Sjostrom (SWE) is the only woman to have won this event four times and is looking to enhance that record.
Imagine being diagnosed with testicular cancer in December 2018, and winning a world championship gold medal just SEVEN months later.
Last night, Nathan Adrian anchored the USA to victory in the 4x100m freestyle relay and became that man.
Click below to see what Caeleb Dressel said to us about his inspirational teammate after.
Katie Ledecky beaten, Adam Peaty's world record and Nathan Adrian's comeback gold medal... was that the best first day of swimming at a World Championships ever?
It's clearly a fast pool, and with Peaty back in the pool for his final today, expect more medals and more drama on Day 2.
As ever, we will be on the ground to give you all the latest news, including another four swimming medals this evening.