Olympic athletes have complained of stinging eyes because Rio organisers have 'over-chlorinated' the outside swimming pool in a bid to prevent it going green.
They say huge quantities of the chemical have been put into the water next to the diving pool which turned a bizarre murky colour overnight.
But now athletes say that the water is damaging their game - and even making them feel nauseous due to the high levels of chlorine used.
Team USA men's water polo captain Tony Azevedo said he could "barely" open his eyes for the final quarter, after their 6-3 victory over France on Wednesday.
"This is the Olympic Games and they are putting so much chlorine in the water that people can't see. You can't have that," he added.
A Rio Olympics source working at the outside Maria Lenk Aquatics outside pool told MailOnline: "The water polo guys are really suffering out there due to the chlorine.
"One member of the US team said he couldn't see a thing towards the end of the game. He was literally blinded because there was so much chlorine in the water. Other guys said the chlorine made them feel sick."
The source added: "The diving pool went green because they [offficials] ran out of chemicals.
"But now they are trying to over-compensate by pouring tons of the stuff into the other [outside] pool and it's making the athletes suffer."
Hungary's Gergo Zalanki said he wasn't sure the levels of chlorine were the only problem with the pool.
"My eyes hurt from the water. It's not good," he said after his team took on Greece in a game that ended in an 8-8 draw.
"It feels like they added more chlorine to the water but I'm not sure. I'm used to it because we have a lot of water like this in Hungary, but I think there might be something else wrong too."
And the Australians complained after their 8-6 victory against Japan.
Australian star Richie Campbell said: "I don't know what's happened. I think they bumped up the chlorine or something because my eyes are stinging.
"It hurts at the end of the game and we'll probably get teary eyes for the next couple of hours but that's alright. I felt it more towards the end. It wasn't too bad in the water but now it's really starting to sting.
"I didn't really notice straight away but you could tell on the TV when we were watching inside. But that's all right, we've probably played in worse pools."
Olympic divers have also had to contend with the green water - but it didn't affect the performance of 3m sychronised divers Jack Laugher and Chris Mears last night as they claimed gold for Britain.
Olympic champion Chris Mears, 23, said the green colour actually may have helped them to victory.
"Oh, the swamp pool!" he laughed, when asked about the furore on ITV's This Morning.
"It was interesting and something I've never seen before. It's not dangerous we've been assured by everyone... and it didn't taste any different - because obviously accidentally you do kind of drink some of the water!
"Also it kind of helped in a way because when you're spinning around sometimes when you're seeing a blue sky and a blue pool it can be quite difficult, but with a green pool it was pretty easy."
Diver Jack Laugher, however, has come up with his own theory about why the water has changed colour - claiming that the ink from the plastic boards surrounding the pool has run into the water.
"We've got some big plastic boards that go into the water just for decoration and effect,' he said. 'But you can see on the waterline that they're blue when below the waterline, and above the waterline it's green.
"And we think maybe a load of ink has run into the pool potentially. It's safe and the doctors have given it the all clear or whatever. And it's different as well, you know, it's another one of those added different conditions."
But Rio Olympic spokesman Mario Andrada said: "We have treated both pools during the night [on Tuesday] and the alkalinity levels have already improved.
"We expect the colour to be back to blue very shortly."
He added: "There's absolutely no risk, no effect for athletes who will compete in the pool."
Despite initial claims from Olympic chiefs that the dive pool was turned green by the algae, they later suggested it could be down to a change in the water's alkalinity.
Mr Andrada said organisers failed to take into account that lots of people would be using the pool - which apparently affects its alkalinity.
"We probably failed to note that with more athletes, the water could be affected," he said. "The people in charge of the pool should have done more intensive tests. We brought in a team of independent experts to check."
Twitter erupted as Tuesday night's synchronised diving final turned into a farce as the pool faded from blue to green.
Rio's aquatic centre is set apart from those of previous years in that it is an outdoor arena, and the green diving pool could be the first failing of the system.
Meanwhile experts expounded their own theories about why the water would change colour, with most opting for algae as the probable cause.
Exposure to sunlight and ultra violent light can break down chlorine-based disinfectants and cause them to evaporate, they said.
Ralph Riley, from the UK Pool Water Treatment Advisory Group, added: "It needs the chlorine disinfectant to be clear, bright, blue and sparkling, so if it's not there, the water could become discoloured."
Other theories suggested the corrosion of pipes, releasing copper or iron ions into the water, could be to blame.
While others, on social media, suggested the discolour might have been caused by an athlete urinating in the water.
Nathaniel Storey, a microbiologist from the University of Reading, told MailOnline: "There are two main possibilities for the green colour of the diving pool - one is from algae, the other is due to copper in the water.
"If the pools aren't adequately treated then an algal bloom can form... Algal spores can be brought in by wind and rain.
"The best way to stop algae is to prevent it in the first place by maintaining a good pool sanitising regime.
"Treatment is more difficult as time goes on but requires either 'shocking' the water with high levels of chlorine, although some algae can be resistant to lower levels of chlorine, or the use of specific algaecidal agents."
He added: "The green algae in pools is unlikely to be harmful in itself, but would instead appear to indicate that the treatment regime in place is inadequate. Therefore the concern would be that other microorganisms that could cause disease could be present."
Dave Richards, head of communications for the British swimming teams, confirmed: "Our athletes competed in the venue yesterday without issue."
Viewers turned to Twitter on Tuesday night to express their confusion with the hashtag #poolgate.
The diving pool at #Rio2016 looks like a pond it's SO green. Wasn't that colour yesterday,' Julie Webber tweeted.
Tom O'Connor wrote: "Does anyone else think the rather green water at the Rio diving pool looks vile?"
Robert Devine joked: 'Olympic diving pool is green due to a reaction with the chemicals and suntan lotion. Happened to our holiday pool #Turkey1999.'
Steve Ellul joked: "That reminds me... Pea and Mint Soup for dinner. #Rio2016 #olympicdiving #greenpool'ue pool on Monday."
Concerns were raised before the Olympics about the quality and cleanliness of the water being used for the rowing and sailing events - but not the pools.