KAZAN, Russia - Katie Ledecky of the United States remains on course to win a fifth gold in Kazan, while a 10-year-old from Bahrain made history on Friday at the world swimming championships.
The 18-year-old Ledecky has been the outstanding performer in the Kazan pool, winning golds in the 200m, 400m and 1,500m freestyle, plus anchoring the US women's 4x200m freestyle relay win.
The teenager has twice lowered her own 1,500m world record in Kazan and clocked the fastest time of 8min 19.42sec in the morning's 800m heats to qualify for Saturday's final.
"I always like to finish on a good night and leave a meet with a nice feeling, so we'll see what happens," said Ledecky, the 800m world record holder and defending champion.
Bahrain schoolgirl Alzain Tareq, believed to be the youngest swimmer to ever compete at a world championships, caused a splash when the 10-year-old swam in the 50m butterfly heats.
She finished last overall of the 64 competitors who raced the event after swimming 41.13sec and was 15sec off the fastest time of 25.43 by Sweden's world record-holder Sarah Sjostorm, who swam in a later heat.
The pint-sized Tareq spent an hour answering a flood of questions in crystal-clear English from the scrum of media, and several of the swimming world's elite commented that they were surprised to see her competing.
US star Missy Franklin, who won six world golds two years ago in Barcelona, is charmed.
"She is so cute and tiny," said the 20-year-old Franklin.
"I haven't had a chance to talk to her so far, but every time I see her she gives me the biggest smile." There is currently no age restriction on swimmers competing at either a world championships or an Olympics and Tareq has said she wants to swim at next year's Rio games.
Franklin, who has won two bronze medals so far in Kazan, was the second fastest through to Friday night's 200m backstroke final.
She clocked 0.67sec behind the 2:07.17 posted by Hungary's 'Iron Lady', Katinka Hosszu, who has already won the 200m individual medley world title in Kazan.
"This is my favourite event and I'm looking forward to the semi-final. It's going to be fun," said Franklin, who set the event's world record in winning the 2012 Olympic final.
Australia's Emily Seebohm, who was seventh fastest through at 2.27sec, is bidding to complete the backstroke double after winning the 100m gold on Monday.
"I'm happy, I didn't want to push it as hard as I could and wanted to save something for tonight," said the 23-year-old.
With reigning world champion Cesar Cielo having flown home to Brazil with a shoulder injury, France's Florent Manaudou was the fastest into the evening's 50m freestyle semi-finals.
He clocked 21.71sec with Olympic 100m champion Nathan Adrian of the US right behind at 0.02sec.
Reigning 100m butterfly world champion, Chad le Clos of South Africa, was eighth fastest, at 0.92sec, into Friday night's semi-finals behind Laszlo Cseh's 50.91.
Cseh beat Le Clos on the wall in Wednesday's 200m final and the pair are set to resume their duel in Saturday's final.
Chinese teenager Li Zhuhao is also in the mix for a medal having swum a world junior record of 51.54 in the heats, just 0.63 slower than Cseh.
"That was very fast, I finished second in this event in Barcelona two years ago and I hope to fight for a medal here again," said Cseh.
There were no surprises in the men's 4x200m freestyle relay as Australia, defending champions the USA, Great Britain, Germany, Poland, the Netherlands, Russia and Belgium all booked their place in the evening's final.