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Why did the Rio Olympics pool water turn green?

Whatever the reason, it seems to have helped Canadians. But don’t expect the water to remain emerald green for long.

The water of the diving pool at right appears a murky green, in stark contrast to the pool's previous day's color and also that of the clear blue water in the second pool for water polo at the venue as divers train in the Maria Lenk Aquatic Center at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Tuesday, Aug. 9, 2016. (AP Photo/Matt Dunham)

The water of the diving pool at right appears a murky green, in stark contrast to the pool’s previous day’s colour—and also that of the clear blue water in the second pool for water polo at the Maria Lenk Aquatic Centre. (AP Photo/Matt Dunham)

Before Meaghan Benfeito and Rosie Filion were about to dive off the 10-metre platform in perfect unison, Canada’s bronze medal-winning duo had one last piece of advice for one another: “Don’t open your mouth in the water, just in case,” Benfeito explained.

The worry? One day prior, both pools at the Maria Lenk Aquatics Centre were a crisp blue. But on Tuesday, the pool reserved for the diving competition was an emerald green.

The cause, according to Rio spokesman Mario Andrada in an interview with The Associated Press, was “a proliferation of algae.” “If it were green and yellow, we would know it was a patriotic thing,” he added.

Andrada can be forgiven if his joke about Brazil’s national colours fell flat, especially since one British diver told media she couldn’t see her dive partner underwater because it was too green.

    Canadian diving team leader Mitch Geller speculated the cause was a broken filter and that algae would multiply faster under the hot Rio sun. “But I’m not sure,” he said. “It’s not really dangerous. It’s not like it’s toxic or dirty or any of that.”

    Athletes were reassured of their safety a few hours later, with officials saying the water was tested and posed no health threats. The culprit, however, was still to be determined.

    Whatever its colour, the liquid in the pool hadn’t morphed into something altogether new, Benefito said. “We know that it’s water down there.” And in an odd twist, the green beneath the diving board may have been to Canada’s advantage. As Maclean’s correspondent Jonathon Gatehouse reported, Filion felt better with green than blue. “During the week, I was having trouble seeing the water, with the blue sky and the sun’s reflection,” said Filion. “So I was like, ‘Hey, it’s green, I can see it.’ It really helped me in my diving. It gave me a lot of confidence.”

    If any other divers hoped to benefit from the contrast provided by the off-colour pool, they may be out of luck. Rio’s spokesperson emphasized that the water will once again turn blue for Wednesday’s competition.

    UPDATE, Aug. 10, 2016: Mystery Solved? FINA, the international governing body for sports such as diving, water polo and synchronized swimming, released the following statement on Wednesday:

    “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. The FINA Sport Medicine Committee conducted tests on the water quality and concluded that there was no risk to the health and safety of the athletes, and no reason for the competition to be affected.”

    But it appears the organizers spoke too soon when they promised the pool would be blue again on Wednesday.

    Day 4 at the Rio Olympics

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