NBC Olympics.com – Divers showing up to the Maria Lenk Aquatics Center on Tuesday were greeted with a shocking sight. The water in the diving pool, which was a pristine, azure blue a day before, turned a deep shade of green overnight.
The adjacent swimming pool was not affected.
Rio spokesman Mario Andrada said he believed that a "proliferation of algae" had been to blame at the Maria Lenk Aquatics Center, while international diving chiefs claimed to be unaware what had created the problem. "It will be blue from now on," Andrada said.
"This was because of heat and a lack of wind," he said. "We did all the chemical tests. The pool will be blue tomorrow (Wednesday).
"If it were green and yellow, we would know it was a patriotic thing," Andrada joked, referring to Brazil's national colors.
Canada team leader Mitch Geller suspected the cause was algae that multiplied quickly in the day's warm and sunny conditions.
"Everybody was scratching their heads going, 'What's going on?'" he said. "I think that the filter is busted, but I'm not sure. It's not really dangerous. It's not like it's toxic or dirty or any of that. It seemed to get worse over the course of the competition."
The kale-colored water wasn't just a cosmetic nuisance; it was so dark that divers couldn't see the bottom of the pool.
"They're used to seeing the water," Geller said. "The visuals are really, really important in diving."
Chen Ruolin, who teamed to win gold with Liu Huixia, said it didn't affect them.
Paola Espinosa of Mexico, competing in her fourth Olympics, noticed the pool getting increasingly darker throughout the six-round competition. But she said the water didn't smell or affect her skin.
"I haven't seen anything like it before," Espinosa said. "But it's Brazil and everything is green down here, so maybe it was a decoration to make it look pretty."
American Jessica Parratto wears contacts and said the water didn't burn her eyes.
Bronze medalists Meaghan Benfeito and Roseline Filion of Canada tried not to laugh as they gazed at the water from atop the 33-foot tower. They liked that the dark green color offered a helpful contrast with the blue sky.
"The only thing we said is don't open your mouth in the water, just in case," Benfeito said.
Geller said a Canadian pool expert was coming in Wednesday and he would offer to help Rio organizers chemically treat the water if there's a problem with the filter.
"I don't know what it's going to look like tomorrow," he said. "I hope it's not a swamp."
American diver David Boudia, who won silver while diving into blue water on Monday, and Great Britain's Tom Daley, who took bronze, were as shocked as anyone.
"Wait is someone playing a joke or are we celebrating St Patty's Day early here in Rio?" he asked on Twitter with an accompanying photo of the green pool.
"Ermmm...what happened?!" Daley tweeted.
The Associated Press contribued to this report