♒ We know that green is Brazil's favorite color, and the Olympics are trying to Go Green for the environment, but even so, the overnight change in color of the Olympic swimming pool from an azure blue to murky green took scientists and sportsmen by surprise. While officials hastened to assure athletes that the green waters posed no health threat, the mystery caused much speculation. Caipirinha-flavored Soylent? Stiffed by Trump’s pool cleaning service? Who peed in the water?
♒ “Midafternoon, there was a sudden decrease in the alkalinity in the diving pool, and that’s the main reason the color changed,” said Mario Andrada, a Rio 2016 spokesman. So, the pool became more acidic. But acidic water is not green. There are two likely explanations: first, excess copper in the water can turn it green, but not murky. The latter is caused by a sudden and rapid growth of algae, triggered by the warm weather, lack of wind, insufficient chlorine and ineffective filters.
♒ Algal spores can enter the water inadvertently, carried by wind, rain and contaminated swimsuits. When the conditions are right, they can "bloom" overnight. Because these algae are visible only under the microscope, there must be millions of them in the water to change the pool color from blue to green. One way to deal with them, after normalizing the pH, is *superchlorination*—aka shocking them with high levels of chlorine. Not all the Olympians are complaining: Canadian divers said that the contrast with the sky helped them win the bronze.
♒ Pix: The Olympic diving pool on August 8 (left) and the Olympic diving pool on August 9 (right) Image: AP