German water expert befuddled by Olympic green pool

Organizing committee spokesman Mario Andrada said in Rio on Wednesday that a decrease in the alkaline level in the diving well led to the green color. He added that the pool for water polo and synchronized swimming was being affected in the same way but "we expect the color to be back to blue very shortly."

DW: How could this have happened?

Alexander Eckhardt: This pool turning green shows that something went horribly wrong. I'm not sure whether the substance that caused the water to turn green is toxic or not - the green color doesn't necessarily mean it's toxic, but I can say that swimming pool water usually doesn't turn green. There might be chemical reasons, perhaps a copper compound, or biological reasons, i.e., bacteria or green algae that were able to turn the water green.

But isn't this water chlorinated? I would expect green algae to die in chlorinated water.

As a matter of fact, they should die. But something went wrong. Maybe the chlorination didn't work properly, or there were just too many algae, or there was a leak. It's difficult to speculate about this if you're 12,000 kilometers away [in Germany] and you have no information about the water treatment system.

In your experience with water safety, have you ever seen anything like this?

No, I must say when I saw the image this morning, my first reaction was: Oops, this doesn't look good to me…

There are two pools, right next to each other. One of them is blue, the other green. Doesn't that eliminate the possibility of copper piping being the cause, assuming that the two pools share the same piping?

You're right. But the same goes for algae. It must come from somewhere. The algae don't grow explosively to the point that a pool could turn green overnight. It must have been there before. The process would take several days.

Don't algae need sunlight?

They do, yes, but since the swimming pool is illuminated very brightly, it might provide enough light for the algae.

There were safety concerns ahead of the Olympics regarding water quality, with reports that if an athlete consumed even three teaspoons, he or she could contract a digestive virus. Is it possible that the green color results from viruses?

No, viruses are not green. And even if they were green, I don't believe that they could accumulate in such an amount that the water would actually turn green. But I'm not a microbiologist.

But it could be bacteria?

Yes, bacteria could result in green coloration.

So, of the three possibilities copper piping, algae and bacteria, which is the most dangerous?

Depending on the chemical, the amount is most likely not enough to pose a real threat. The bacteria and algae, however, can cause digestive issues. The human body is not used to consuming these things. But they could also be harmless.

If these Olympics were in Germany, and you - or your agency - were in charge of water safety in the swimming pools, would you allow people to use the green pool?

No, because as yet we have no information about the reason for the green color.

Dr. Alexander Eckhardt is a toxicologist who works in the water safety department at Germany's Environment Agency. His specific field is monitoring the safety of drinking water and swimming pools.