China’s Lin Yue and Chen Aisen, left, compete in a men’s synchronized diving final on Monday, a day before the diving-pool water turned green for competitors including Brazil’s Ingrid Oliveira and Giovanna Pedrosa, right, in a women’s diving final. Photo: MATT DUNHAM/ASSOCIATED PRESS

Green was an unexpectedly popular color yesterday and today at the Summer Olympic Games in Rio de Janeiro where an indoor pool used for diving turned murky green overnight. The deep green color stands in sharp contrast to the usually clear blue water, which existed in normal conditions in an adjacent pool used for water polo and synchronized swimming.

The diving pool was clear blue on Monday, but apparently turned green overnight, according to multiple media sources. It became so dark that divers could not see the bottom of the pool, possibly affecting performance.

It was originally reported via a statement from Olympic organizers that the reason for the color change was unknown. Now, according to the Associated Press, Rio spokesman Mario Andrada blamed the green water on “a proliferation of algae.”

"This was because of heat and a lack of wind," he told the AP.

Ralph Riley, vice chairman of the U.K.-based Pool Water Treatment Advisory Group told that lack of chlorination could have allowed algae to enter the pool, causing it to turn green. Sunlight and high temperatures can deplete a pool’s chlorine, he added.

Andrada insisted that Olympic organizers ran all necessary chemical tests to ensure the safety of the green water for the Olympic athletes. This was confirmed to the AP by multiple athletes, each telling the press organization that the water did not smell, affect the skin or burn the eyes.

A Canadian pool expert was expected today to help Rio organizers chemically treat the water, especially if there's a problem with the filter, the AP reported.

This green pool water issue comes amid major problems with water quality in the Brazilian oceans and bays used for aquatic events like sailing, rowing and open water swimming.

Extreme water pollution is common in Brazil—and Latin America in general—where the majority of sewage is not treated. Fernando Spilki, a virologist at Feevale University in Southern Brazil, told Laboratory Equipment that sewage treatment is less than 50 percent for 30 million people in the country. Therefore, all the water from toilets, showers and sinks is released into bodies of water like Guanabara Bay, Rodrigo de Freitas lake and the water surrounding Fort Copacabana–all Olympic venues.

As a result, Olympic athletes are almost certain to come into contact with disease-causing viruses that in some tests measured up to 1.7 million times the level of what would be considered hazardous on a Southern California beach, according to a year-long investigation by the AP.

There have been complaints, but nothing drastic so far. However, the open water swimmers—who are most at risk—do not compete until Aug. 15 and 16.

Sean Anderson, an environmental studies professor at California State University Channel Islands, expressed disappointment—but not shock—to Laboratory Equipment when discussing the situation.

“Controlled pool conditions are easy to get right,” he said. “The same folks, the Rio Olympic committee, said [the green water] was okay. But its those same people that are saying the water quality in Guanabara Bay is also okay.”