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Olympic mystery! Why did pools in Rio go green?

As it turns out, it’s pretty easy being green.

Olympic organizers scrambled to answer just how they let a pair of outdoor Olympic pools in Rio turn green. It began Tuesday when, apparently overnight, the azure blue waters of the diving pool had turned into a swampy shade of green.

WATCH ON NBCOlympics.com: Why algae in competition pools are frustrating Olympic athletes

A day later, the adjoining pool used for synchronized swimming and water polo matches began transitioning into a similar shade.

AP, Reuters
The diving pool as it appeared Monday, on the left, and then a day later.

“I have no idea what the green pool is other than if Shrek has been in the pool and had a bit of a swim,” said British diver Tom Daley, who earned a bronze medal in men's synchronized 10-meter on Monday, when the pool was still clear blue.

Olympic officials originally blamed the discoloration on a “proliferation of algae” caused in part by “heat and a lack of wind.” They later said they pinpointed the problem: They ran out of chemicals for the water tanks used to treat the pool.

That caused a drop in alkalinity, leading to the discoloration of the water.

Adam Pretty / Getty Images
A lifeguard sits by the edge of the diving pool Tuesday at the Maria Lenk Aquatics Centre in Rio.

However, they let competitions move forward, saying the water remained safe.

“There is absolutely no risk whatsoever for the health of anybody, especially for the athletes or anybody,” said Rio spokesman Mario Andrada. “An independent group confirmed our assessment.”

Matt Dunham / AP
Competition continues at the diving pool, despite the mysterious color change of the water.

But several athletes complained Wednesday that efforts to treat the water were actually making things worse.

“I could barely open my eyes for the final quarter,” Tony Azevedo Team, the captain of the U.S. men’s water polo team, told reporters following the team's 6-3 victory over France. “This is the Olympic Games and they are putting so much chlorine in the water that people can’t see. You can’t have that.”

RELATED: What makes your eyes red in the pool? It's not the chlorine

But American divers Sam Dorman and Michael Hixon, who dove earlier this week in the green-tinged water, had fun with the unusual situation.

“Kermit the frog had a bath the other day. What can you say?” Dorman told TODAY on Thursday. “It’s something out of our control. We can’t do anything about that.”

Hixon noted the unusual color may have actually helped his sense of perspective during competition.

“I just thought it was advantageous for us,” he said. “Under the lights, that green was pretty bright so our visual cues were easier.”

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Striking images from the Rio Olympics

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Striking images from the Rio Olympics

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