London triathlon world championship series - in pictures

The Serpentine in Hyde Park isn't renowned for balmy temperatures, even in the middle of summer, as these two Australian athletes soon realise after going for a quick dip before the race begins Photograph: Tom Jenkins/Tom Jenkins

The goggles are on as the elite athletes prepare to dive in .... Photograph: Tom Jenkins for The Guardian

Perhaps they've just seen this sign warning against the dangers of blue green algae Photograph: Tom Jenkins for The Guardian

In they go ... Photograph: Tom Jenkins for The Guardian

The elite men follow suit, with current world champion Javier Gómez from Spain nearest the camera Photograph: Tom Jenkins for The Guardian

In the amateur race, every extra inch could count. They'd better hope the officials aren't looking Photograph: Tom Jenkins Tom Jenkins for The Guardian

The Houses of Parliament can be seen in the background as the competitors begin their swim Photograph: Tom Jenkins for The Guardian

Not much space and plenty of splashing in the amateur race Photograph: Tom Jenkins for The Guardian

The elite men, having emerged from the water ... Photograph: Tom Jenkins for The Guardian

... then run through sprinklers in the transition area on their way to collect their bikes Photograph: Tom Jenkins for The Guardian

Some of the amateurs can barely drag themselves out of the water. This chap is suffering from what look like rather excruciating cramp Photograph: Tom Jenkins for The Guardian

The leading pack of elite men cycle out of the transition area Photograph: Tom Jenkins for The Guardian

Britain's Alistair Brownlee grabs his bike ahead of Russian triathlete Alexander Brukhankov Photograph: Tom Jenkins/Tom Jenkins for The Guardian

The elite women zip through Hyde Park Photograph: Tom Jenkins for The Guardian

Looks like these passersby are keen to get involved Photograph: Tom Jenkins for The Guardian

Annamaria Mazzetti of Italy douses herself with water after beginning the final leg on foot Photograph: Tom Jenkins for The Guardian

The lead pack of elite female runners, led by Britain's Helen Jenkins, run along the bank of the river Photograph: Tom Jenkins for The Guardian

Jenkins crosses the finishing line first to win the elite women's race Photograph: Tom Jenkins for The Guardian

And then collapses to the floor Photograph: Tom Jenkins for The Guardian

And she's not the only one. Melanie Annaheim of Switzerland goes down at the finish next to the exhausted Lisa Norden of Sweden Photograph: Tom Jenkins for The Guardian

Annaheim has to be carried away for medical help Photograph: Tom Jenkins for The Guardian

It's a gruelling business. Here, Nicola Spirig of Switzerland (left) and Ai Ueda of Japan try to catch their breath Photograph: Tom Jenkins for The Guardian

At least one person looks full of beans as he crosses the finish line. Alistair Brownlee, an Olympic medal hope for Team GB, was so far ahead of his rivals in the men's race he walked the final few metres and high-fived the crowds. His brother Jonathan Brownlee came in third Photograph: Tom Jenkins for The Guardian