THE course record at this year's Henley Classic swim was shattered by five seconds.
Great Britain open water swimmer Caleb Hughes set the fastest time of 24 minutes and 14 seconds on his way to victory in the elite men's category
About 750 people took part in the 2.1 km swim on the Henley Royal Regatta reach, starting at 4.30am on Sunday.
There were competitors from South Africa, America and Australia but defending champions Alex Studzinski and Beatrix Eisel were not be racing due to the German national trials taking place at the weekend.
Hughes, 19, who will compete in the world championships in Kazan, Russia, later this month, beat rival Tom Allen by a fraction of a second.
Both men ducked under the previous course record of 24 minutes and 19 seconds set by Studzinski.
Hughes, a student at Loughborough University, said the swim was a ?bit of fun? but added: ?It was quite tight between me and Tom and it wasn't as clear cut as I thought it was going to be. I guess you can take things from every race.?
The elite ladies title was taken by another GB athlete, Fern Davies, who broke her own course record as she finished in 27 minutes and two seconds.
Swim co-founder Jeremy Laming said: "I was very proud of how the event went. It?s no exaggeration to say that every year we host it, the quality of the competition gets ever more exciting and is now genuinely world class.?
He said it was good to see a wide range of swimmers taking part.
?What people really love about it is that they can swim on the same water as athletes of the calibre of Caleb and Tom.
"It's about getting everyone out there and enjoying the water. We have 70-year-olds who like to swim the course.?
Former Leander Club rower Matt Baker finished third in the open men?s category.
Henry Bell, from Rotherfield Peppard, came third in the junior men?s category.
Vassos Alexander, who appears on Chris Evans' BBC Radio 2 breakfast show, took part in the swim.
He later tweeted: ?What a way to start Sunday - gentle 2km, 4am swim in the Thames as the sun rises over Oxfordshire. I've been energised all day.?