Germany's Kristina Vogel beats New Zealander Natasha Hansen in the final heat.

The six victors, including Britons Becky James and Katy Marchant, go into the quarter-finals, with the losers going into the repechage.

Adrian Moorhouse
1988 Olympic 100m breaststroke champion on BBC TV

There is quite a lot in this water but we have been assured there are no man-eating fish - no piranhas or sharks.

Good to know.... 

Image source, Reuters

Russia's Anastasia Voynova beats China's world champion Zhong Tianshi by 1/1000th of a second in heat number five. Thrilling.

The Netherlands' Elis Ligtlee, who has already won keirin gold in Rio, beats Lithuania's Simona Krupeckaite on the line in heat four.

GB's Jodie Williams: "I've been struggling a bit all year but I'm happy with my run.

"It should be good enough to go through and I'm looking forward to it.

"I'm finally an Olympian. I've wanted it for the last four years after missing out on London 2012."

Australia's 2012 Olympic gold medalist Anna Meares goes in heat three, after needing a repechage to get here.

And she needs a repechage again if she's to reach the quarter-finals after losing to Hong Kong's Lee Wai Sze, who beat her on the line.

Image source, Reuters

Just over the hour mark in the women's 10km swim just off the coast of Copacabana Beach. 

Britain's Keri-anne Payne is about 15th at the half way stage but has just made up about 10 places by not visiting the feeding station. Interesting tactic. 

This pack has been pretty tight, no one has really made a break yet. 

Payne's coach is expecting someone to make a break at about the 7500m mark and that's not for about another 30-35 minutes. 

GB's Jodie Williams runs a season's best as she finishes third in her 200m heat. She'll have to wait to see if she gets through as a fastest loser as only the top two in each heat go through automatically.

Williams runs 22.69 is the fastest of the losers so far with two heats to go so she should progress.

Image source, Getty Images

Germany's Miriam Welte catches Katy Marchant napping and makes her break much earlier in the race than the Briton had anticipated. 

But on the final lap, Britain's Marchant is closing, closing, closing and just wins on the final straight.

Second heat sees Britain's Katy Marchant face Miriam Welte of Germany.

This is such a strange spectator sport, proper cat and mouse. Virginie Cueff and Becky James stop for a while as they try to gauge each other - they're allowed 30 seconds without moving - but they're back going at it now.

Britain's James just squeezes ahead on the home stretch and goes through, but not as comfortably as she might have expected.

She's through to the quarter-finals. France's Cueff goes into the repechage. 

Becky James v Virginie Cueff over three laps in the 1/8 round is just about to begin.

GB's Dina Asher-Smith: "I was really happy. I was a bit nervous but you always want to get through to the next round. I'm excited for the semi-finals.

"I thought I'd be worse with nerves. It's my first Olympics but it's also a competition. Racing is something I do day-in day-out. 

"I'm happy to finally get under way."

Kerri-anne Payne still in the mix in the swimming. We're 53 minutes into the race now. For context, London 2012's medalists took just under two hours to finish, but our pundits think this one might take longer.

It's almost time for the cycling, first up will be Great Britain's Becky James v Virginie Cueff in the women's sprint 1/8 finals.

Cycling starts at 14:00 BST.

Team GB's Dina Asher-Smith makes it through to the next round of the women's 200m after finishing second in her heat. The top two automatically qualify and her compatriot Jodie Williams will be going  in heat seven at 14:06 BST.

GB's Lani Belcher and Angela Hannah are through to the women's kayak double 500m semi-final, despite having finished last in their heat.

Amid a blur of paddles and splash, Britain's Jess Walker finishes fifth in her heat with a time of 41.123 seconds to qualify for the semi-final later on Monday.

BBC One

If you're watching on the TV, it's time to switch from BBC Two to BBC One.

Right, let's go through which Britons are in action or will be over the next few hours:

Athletics

Sophie Hitchon is in the hammer final. Dina Asher-Smith and Jodie Williams are in the women's 200m heats, while Rob Mullett goes in the steeplechase heats. Sebastian Rodger and Jack Green are involved in the men's 400m hurdles.

Badminton

Chris Langridge and Marcus Ellis face Japan's Hiroyuki Endo and Kenichi Hayakawa.

Canoe Sprint

Jess Walker goes in the women’s K1 200m heats.

Cycling 

Rebecca James and Katy Marchant go in the women's sprint 1/8. 

Mark Cavendish is in men's omnium action, while Laura Trott goes in the equivalent women's race.

Equestrian

Fiona Bigwood, Carl Hester and Charlotte Dujardin go in the individual dressage.

Swimming

Keri-anne Payne is in the women’s 10km race right now.

Synchronised Swimming

Olivia Federici and Katie Clark take part in the duet technical routine.