The Rio Olympics’ official Twitter account says the water has been tested and poses no risk for athletes. A further investigation is underway.
But that won’t stop the internet from taking some guesses as to what could cause the discoloration. Here are a few.
It’s algae
The Olympic diving pool is kept warmer than the one with the lap lanes. That means it’s a bit more of a friendly environment for microbes to grow in, as Sports Illustrated points out. But then, there ought to be enough chlorine in that pool to kill the algae. Ought to.
It’s oxidized copper
Think of the Statue of Liberty’s patina: When its copper was exposed to water, it began to oxidize (i.e., rust). Unlike iron, which turns brown when it oxidizes, copper turns green. But then how would copper get into the pool to oxidize? Is a pipe corroding?
Gizmodo cites a section of a handbook on pool chemistry that reads:
Copper can enter the pool water from corrosion or galvanic activity in copper heaters, from Chapter 2: Chemical Factors – Stain Producing Minerals 18 Notes: copper-based algaecides and from the source water. Copper problems are often indicated by pool water with a true clear green color, whereas green water caused by algae would be green and cloudy.
It’s urine
It’s very likely not urine. That would be a lot of urine — too much to turn a pool green that’s more than 15 feet deep. (It would have to be the really, really yellow variety of urine, right?)
As Vox’s Libby Nelson explained, it was the water quality in Rio’s outdoor venues that had people worried before the games began:
The pollution in Rio’s waterways is serious: The locations for the rowing and sailing races are ridden with viruses that could sicken athletes if they inadvertently end up swallowing water, according to an investigation from the Associated Press. Five times in the past 13 months, Copacabana Beach, where the marathon swimming and triathlon will take place, had so much rotavirus in the water that if it were located in California, it would have had to post water quality warnings.
No one thought the swimming and diving pools would pose a problem. And perhaps it’s not a big deal, considering the officials say it’s safe. But the bigger question is: Will athletes want to compete in it?
http://www.vox.com/2016/8/9/12417804/rio-olympics-2016-pool-green