Most Olympic attention goes, deservedly, to the athletes. No matter how strange or dramatic a stadium design, it’s never as grabby as the world’s top-tier swimmers, runners, and leapers.

Yesterday, though, one piece of Olympic infrastructure decided to put on a show of its own. Sometime in between the men’s synchronized diving finals on Monday and the women’s on Tuesday, the diving pool at the Maria Lenk Aquatics Centre transformed from a crystal blue into a deep, murky green.

This was no slight tinge, either. Athletes reported that, when immersed, they couldn’t see their diving partners. Observed beside the neighboring water polo pool, it looked downright sinister, like the Wicked Witch of the West standing next to Glinda.

Those in charge appeared as flummoxed as anyone else. As the New York Times put it, “Officials released a brief statement that did not address the main questions: What had happened, why had it happened so quickly, and why wasn’t there a simple explanation, given that this is the sort of thing that commonly happens to swimming pools?”

Although they assured everyone that the water was still clean, top brass refused to take any questions from the news media, which responded by taking matters into their own hands: Gizmodo has diagnosed it as an algae bloom, which New Scientist thinks means it ran out of chlorine.

Meanwhile, the divers kept diving. “We got a personal best score,” American diver Jessica Parratto told the Sydney Morning Herald. “Maybe we should ask for a green pool from now on.”

Every day, we track down a fleeting wonder—something amazing that’s only happening right now. Have a tip for us? Tell us about it! Send your temporary miracles to [email protected].