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On Tuesday, Olympic officials attributed the extremely green diving pool to a “proliferation of algae,” caused in part by “heat and a lack of wind.” Today, after the water polo and synchronized swimming pool also turned green, officials clarified that the issue was a drop in alkalinity in the pools. As explained by FINA, the international swimming federation:

FINA can confirm that the reason for the unusual water colour observed during the Rio 2016 diving competitions is that the water tanks ran out some of the chemicals used in the water treatment process. As a result the pH level of the water was outside the usual range, causing the discolouration.


Keeping pools clear is much more complicated than simply pouring in some chlorine. It involves filters, sodium bisulfate, acid, ozone, chlorine, and other chemicals. Alkaline substances are used to help keep the pH level—the measure of acidity of the pool—stable. If the alkalinity and pH are at proper levels, the chlorine effectively kills algae and other bacteria, and what it doesn’t is caught by the filters. Any one of these systems being out of balance affects the others.

The pH level begins to vary when alkalinity is off, so acid is needed and chlorine is less effective at killing algae. It is likely that Rio officials tried to solve the problem in part by “shocking” the pools with chlorine, given that American and Australian water polo players complained about burning eyes.

Now that the alkalinity problem has been identified, officials say the pools will be clear again on Thursday. The pool used for the swimming competition is indoors in a different venue, and thus far hasn’t seen any problems.

Olympic water polo played in greenish water. Photo credit: Tom Pennington/Getty

The Maria Lenk Aquatic Center, where diving, water polo, and synchronized swimming are being held, was opened in 2007 and taken over by the Brazilian Olympic Committee in 2008, after which renovations were made. A test event was held in April and the pool was closed until the Olympics, giving officials three months to make any last minutes changes, though they didn’t specify whether any were needed.

To get a sense of how they would’ve prepared the venue for the Olympics, I spoke with Rafa Escalas, a Spanish former Olympic long-distance swimmer who now owns a swimwear manufacturing company. More saliently, he served as the competition manager for swimming at the 1996 Olympics in Atlanta. Held at the newly built Georgia Tech Aquatics Center, they were held outdoors, with a roof over the pool and open sides.

The Georgia Tech Aquatics Center a year before the Olympic Games. Photo credit: John Bazemore/AP

The test event for the pool was the 1995 Pan Pacific Swimming Championships, held the year before. According to Escalas, the biggest issue discovered during the Pan Pacs was that the natural light was wreaking havoc on NBC’s camera shots. For the actual Olympics, screens were placed on two ends of the pool to block the light, and in 2003, Georgia Tech had the entire facility enclosed.


The green water is affecting NBC’s shots at these games, too. While not as important for diving—though the underwater shots from the 10 meter platform competition can be cool—underwater cameras show great images during water polo that the typical observer wouldn’t see. Sometimes too great of images.

Per the current FINA facilities rules, pools for swimming must be heated to between 25 and 28 degrees celsius, with no variation once the Games begin; not less than 26 degrees for the water polo and diving pools; and not less than 27 degrees for the synchronized pools. Escalas remembered the exact temperature the Atlanta swimming pool was set to: 25.3 degrees.


During the Pan Pacs, organizers decided after numerous discussions and meetings that the Atlanta weather wasn’t going to have a large effect on the temperature of the pool, though they did choose to install a new $200,000 cooling system in the warm-up pool because it got too warm. If Atlanta had been hit by a heat wave during the Games, the plan to cool the pool—I shit you not—was to put giant ice cubes in it overnight. Luckily that wasn’t necessary.

Providing equipment for the Olympics is a very big deal. Astral sand filters, for instance, were purchased for the Georgia Tech pool at heavy discount. In exchange, Astral can advertise that they are the official sand filter provider of the 1996 Olympic Games. An Astral employee was flown over from Spain for the duration of the Games to monitor the system and make it worked properly. As Escalas explained it, equipment was purchased from all over—lane lines from Sweden, starting blocks from Italy—to have the best possible equipment.


Rio 2016 spokesperson Mario Andrada blamed the green pools, in part, on the number of athletes using them. “We probably failed to note that with more athletes, the water could be affected,” he said. But that explanation doesn’t square with what Escalas told me. “At weekend swim meets with 1,000 people,” Escalas said, “you will not have the [same] clear water on the first day as the last day of the meet.” But that shouldn’t happen at the Olympics because, comparatively, it is a relatively small meet, with fewer competitors and events spaced out for television.

One of the most important jobs for the aquatics venue manager is to make sure the water is clear and safe, Escalas explained, because once it turns green there is no quick and easy fix. The full Olympic schedule means pools can’t be shut down for the day, and they’re used from morning until night. Chemicals can’t be dumped in willy-nilly because the athletes will be negatively affected, and extra filtration cannot be installed on the fly.


“The fastest way is to take out green water and put in clear water,” said Escalas. “For example, the pool in the [United States Olympic] Trials was filled up by the fire department. They don’t turn on a faucet and go.” In an absolute worst case scenario? “Theoretically, they could empty the pool and get the fire trucks.”

If Rio organizers are correct and they’ve solved the problem, such drastic measures won’t be necessary. But until the water is once again crystal clear, they will be feeling immense pressure. “I’m sure they are sweating bullets,” said Escalas.


Correction: This post originally stated that the last time Olympic aquatic events were hosted outdoors was in 1996. They were also outdoors during the 2004 Olympics in Athens.

Reporter at the New York Times

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