Pictures of the water in the diving pool has led to a mass of internet speculation as to the causes of a sudden change in colour

This article is more than 4 years old

This article is more than 4 years old

It was the question that dominated the diving events at the Maria Lenk Aquatic Centre in Rio de Janeiro on Tuesday.

What has turned the Olympic diving pool green?

Tom Daley, the British diver, shared an image on Twitter on Tuesday that showed it to be a definite shade of green – particularly in comparison to the pristine water polo pool on the left.



“Ermmm...what happened?!” tweeted the bronze medalist.



On just Monday, the two pools had been the same azure shade, prompting speculation on social media – and at the games – over what could have happened overnight.

Green pool does not bother Tonia Couch and Lois Toulson at Rio 2016 Read more

The mystery overshadowed coverage of the women’s synchronised diving finals at the aquatics centre on Tuesday, with the Guardian’s Owen Gibson reporting from Rio that the cause of the change was not known but there was no risk to athletes.

Owen Gibson (@owen_g) Green water update: Rio 2016 say they've tested the water and there's no risk to athlete health. They're investigating further. That is all.

Owen Gibson (@owen_g) Green water latest. I'm at the venue. No one really knows but it might be something to do with a lack of chlorine.

Britain’s Tonia Couch told Gibson that the pool appeared to turn an ever-darker hue the longer the 10m platform final went on, and prevented her from seeing her partner, Lois Toulson, underwater.

The pair eventually finished fifth.

A spokesman for the Rio 2016 organisers said water tests had been conducted and there was found to be “no risk whatsoever” to athletes, though the cause of the colour change was still being investigated.

Rio 2016 (@Rio2016_en) The water quality at the Maria Lenk Aquatics Centre was tested and there were no risks for the athletes. We are investigating the cause.

An official statement on the cause for the colour change is understood to be being prepared by the organising committee for imminent release.



But organisers’ assurances were not enough to put to rest the speculation that abounded on social media, amidst persistant concerns for the athletes’ safety.

Dom Bevan (@Domboyo) This pool will sort the women from the lagoon creatures #Olympics #diving #greenpool

Michael Hardy (@MichaelHardy21) There is no threat to the athlete's health... unless they plan on having children or living past 30 #greenpool #Rio2016

Dan Walker, a presenter for BBC Sport, ran a Twitter poll to gauge his followers’ thoughts on an explanation for the change in colour.

An overabundance of algae – often indicated by cloudy green water – was thought the most likely culprit in the highly unscientific poll of 3,690.

Dan Walker (@mrdanwalker) No-one will give an explanation for the green diving pool. An official statement from Rio2016 is being prepared!!!

It was considered more probable than the suggestion that the pool had been dyed to match the green of one half of the Brazilian flag.

“Maybe they just wanted to match the colour scheme? And on the bright side, at least it’s not yellow!” tweeted another user.

A Brit following along with the Games looked closer to home for an explanation.

Charley Nicholls (@CharleyNicholls) @mrdanwalker fake tan. I'm from Essex, I recognise water that colour!

Guidelines from Jim’s Pool Care – a mobile pool servicing franchise based in the home of clear blue water, Australia, that specialises in “green pool recovery” – advised that a build-up of algae and contaminants can cause a change in colour.

Brett Blair, a national manager of Jim’s Pool Care, was contacted by Guardian in Sydney for further analysis – or, as he put it, “crazy speculation”.

“It’s a very curious one, because the main reason a pool normally goes green is lack of sanitation,” he said.

He said it was possible that the pool’s filtration system may not have been able to handle a pool of that capacity, or may have failed.

Another possibility was an abundance of phosphates in the water, which are a food source for algae that can feed on bodily fluids such as sweat and urine.

The good news, said Blair, was that this particular colour change was unlikely to be caused by urine.

“It’s way too big,” he said of the Olympic pool.

More good news was that it is likely to be easily counteracted with the addition of chlorine or other chemicals.



“My gut feeling is that it will be cleared up over the next 24 to 48 hours.”

YourPoolHQ (@YourPoolHQ) #Rio2016 Might we recommend some algaecide and shock!?! https://t.co/lEG67csdx9 #greenpool pic.twitter.com/NfV65gp5L0

But, Blair said, “it was not a good PR thing” for the Olympic Games.

“The scary part is how at a world event, a pool could go green. It’s unbelievable.”

That was one person’s entire job, suggested the Guardian.

“You just had to make sure the pool was okay,” agreed Blair. “Where is that guy? Where is the guy looking after the pool?”

Another possibility is that blueish-green but clear water can indicate the presence of copper ions and an unbalanced pH level.

That theory sent Gizmodo and other media outlets digging through online handbooks on pool chemistry.

Either way, bleach is not an advisable solution to the problem – despite Clorox’s attempt to join in on the fun being had on Twitter.

Clorox (@Clorox) Pools have bleachable moments too #greenpool #Rio pic.twitter.com/kyaQjE2yfD

Grant (@SnowAndBeach) Just waiting for Shrek to come out of the swamp that is the Rio diving pool!#Rio2016 #diving #GreenPool #BBCRio2016 pic.twitter.com/EzMsohFBzJ