Gergo Zalanki, representing Hungary in waterpolo, said he wasn't sure the levels of chlorine were the only problem with the pool.

"My eyes hurt from the water," he said. "It's not good.

"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.

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."

Commentators could only speculate as to what had caused the "green abyss", as the BBC team termed it, while spectators channelled their alarm on social media.

Theories from algae to urine were offered up on social media and, while Olympic organisers assured the public the water was safe for competition, they admitted they were unsure what the cause was.