The water in a second Olympic swimming pool mysteriously changed colors on Wednesday much to the chagrin of swimmers and officials at the Maria Lenk Aquatic Center in Rio de Janeiro.

Now the pool used for water polo and synchronized swimming joins the Olympic diving pool in containing uninviting swamp green water.

First, it was thought that algae caused the green color but Rio 2016 spokesman Mario Andrada rejected that assessment: “Midafternoon, there was a sudden decrease in the alkalinity in the diving pool, and that’s the main reason the color changed.”

Some on social media outlets suspected the sudden change in pool color may have been a product of the athletes using the pool as a urinal.

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Nate Hernandez, the director of aquatic solutions at pool care company VivoAquatics, dispelled the notion that urine discolored the water in the pool, the New York Times reported. “To be honest, people pee in the pool all the time — this wouldn’t affect it,” he explained.

Andrada admitted that the water had not been monitored as well as it should have been and that a rain storm in the morning on Wednesday contributed to the problem. “We probably failed to note that with more athletes, the water could be affected… The people in charge of the pool should have done more intensive tests. We brought in a team of independent experts to check.”

Hernandez was not impressed by Rio pool care officials being so unprepared for an Olympic event, which customarily gathers a large number of swimmers.

“Take a pool like the Hard Rock in Las Vegas,” he said. “On a Sunday in the summertime, we’ll put 5,000 people in that water at one time. The most we’ve ever had is about 8,200, and it has never turned green.”