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We Finally Know Why The Olympic Diving Pool Turned Green

Ew. Photo credit: Getty images
Ew. Photo credit: Getty images

For nearly a week now a mystery has surrounded the Olympics and it wasn’t what country would reign supreme: why did those pools turn green?


Officials have run the gamut on possible explanations, including algae bloom and a chemical imbalance caused by too many people using the pool. Now, Olympic officials are handing out a final verdict on what caused the pools, which should’ve been all prepared for a Summer Olympics but weren’t, to turn murky and green seemingly overnight.


Somebody made a mistake.

According to the New York Times, somebody accidentally added 160 liters of hydrogen peroxide on Aug. 5 to the pool used for diving, which neutralized the chlorine and caused it to turn green. Basically, eliminating the chlorine allowed for the growth of “organic compounds,” including what might’ve been algae.

Hydrogen peroxide can be used as a cleaning agent for pools, but not when combined with chlorine. The former neutralizes the latter, which doesn’t help when electronic monitoring systems have to measure the amount of chemicals in the water.

Gustavo Nascimento, director of venue management for the Rio Olympics, said in a news conference that the monitors did pick up the chlorine, but failed to notice that it was no longer working.


So before the synchronized swimming event on Sunday, where athletes kind of need to see each other underwater in order to perform, officials said they had plans to drain the 3.7 million-liter pool and replace it with clean water from a nearby practice pool.

Luckily they were able to clean it. Photo credit: Getty images
Luckily they were able to clean it. Photo credit: Getty images

By Sunday, according to NBC, the pool was back to its correct color. So the medium in which athletes, some who traveled thousands of miles to compete, can perform and show off what they’ve trained years for, is now back to a state where it won’t harm or hinder their results in any way, which is a good baseline for the Olympics.

Officials are of course embarrassed by the instance.

“Of course it’s an embarrassment,” said Mario Andrada, a spokesman for the Rio Games. “We are hosting the Olympic Games, and athletes are here, so water is going to be an issue. We should have been better in fixing it quickly. We learned painful lessons the hard way.”


[The New York Times]

Weekend editor and night person at Gizmodo. More space core than human.

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I’m sorry, I still don’t buy it. Neutralizing the chlorine doesn’t cause an entire pool to turn that shade of green practically overnight, just from dirt, oils, bacteria and algae. Aquariums blasting the light all the time take weeks before they start to grow that much algae.

But, +1 for them admitting the divers were diving into neutralized-chlorinated water, which means plain old fashioned dirty water.