The water in the Olympic diving pool is suddenly very green and no one knows why.

On Monday, the men’s synchronized platform diving events saw teams of two from around the world jump, twist and flip through the air in perfect unison and into the crystal blue water of the Rio Olympics diving pool.

On Tuesday, the women competing in the women’s synchronized 10-meter diving final arrived to find that that same pool is now a very, very unsettling shade of green.

Journalists, spectators, and athletes including Great Britain’s Tom Daley, who along with his partner Daniel Goodfellow, won the bronze medal in Monday’s men’s synchronized event started posting photos and questions on social media showing the diving pool, which looks like a murky lake, next to the water polo pool, which appears clear and blue.

American diver David Boudia, who dove into blue water to win silver on Monday, tweeted, “Wait is someone playing a joke or are we celebrating St Patty’s Day early here in Rio?”

The difference is even apparent underwater, as shown by Deadspin‘s graphic below:

Rio Olympic officials have been far from helpful when it comes to offering an explanation as to the color change.

While no formal explanation has been given, many believe the color change to be the work of an algae bloom indicating that there is not enough chlorine in the pool. Which would be fair enough if it happened in your pool at home, but considering the superbacteria that was found in Rio’s aquatic venues before the games began, if that were the case it would be a huge mistake.

Organisers still can say for sure what caused the color change but they can comment on the water’s safety.

“Water tests at Maria Lenk’s Aquatic Park were conducted and there was found to be no risk to the athletes’ health,” an official reportedly said to BBC Sports’ Nick Hope on Tuesday afternoon. “We’re investigating what the cause of the situation was, but we are happy to report that the competition was successfully completed.”

So for now, the color change remains a mystery. Though I’d like to throw a guess in the ring. When I was a kid my swim coach said that he had put a chemical in the pool that would make the water turn green if you peed. My guess is that divers are a big bunch of poo pee-ers.

Feature image via Tom Daly Twitter