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Water Turned Green in Olympic Pools Because Someone Dumped Hydrogen Peroxide in Them

The chemical neutralized the chlorine in the water, making it possible for "organic compounds" to grow.
Photo by Christopher Hanewinckel-USA TODAY Sports

Officials have finally figured out why the pools in Rio, most notably the diving pool, turned green early this week. Speaking at a press conference, Gustavo Nascimento, the director of venue management in Rio and Mario Andrada, an Olympics spokesman, told reporters that someone mistakenly dumped about 160 liters of hydrogen peroxide into the water last Friday. The hydrogen peroxide reacted with the chlorine in the water, cancelling it out, and allowing "organic compounds"—possibly algae, but they did not specify—to grow once athletes started using the pool.

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Hydrogen peroxide is a perfectly plausible pool-cleaning agent, Mr. Nascimento said, except when it combines with chlorine.

"The electronic monitoring system that measures the amount of chlorine in the water was betrayed by this chemistry," Mr. Nascimento said. So while the monitors showed that there was a proper amount of chlorine in the pools, he explained, they failed to pick up on the fact that the chlorine was no longer working.

Even though they know the problem now, the only available fix is to drain the pool completely and re-fill it with clean water from a nearby practice pool. On top of the athletes complaining that the water was hurting their eyes, it was also cloudy and seeing underwater was virtually impossible, a necessity for a sport like synchronized swimming, which is scheduled to start Sunday. So, they have no choice but to drain the 3,725,000 liters of water in the pool and replace it. Nascimento estimated that the draining process would take six hours, and it would take another four hours to refill the pool.

Andrada called the process "an embarrassment" and apologized for how long it took them to figure this mystery out. "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." They did not lay any blame on a specific person, but apparently a local pool worker made an honest mistake.

[NY Times]