The strange phenomenon is visible to anyone viewing the swimming and diving pools, which sit next to each other like a before-and-after picture. While the swimming pool has maintained its healthy blue hue, the diving pool has turned a viscous green, leading Britain’s synchronized diver Tonia Couch to complain she couldn’t even see her partner under water.
Experts and journalists have posited theories to explain the greenness—is it from copper ions? An algae bloom? Insufficient chlorination? A Rio 2016 spokesperson says officials are investigating. Whatever it is, it looks pretty gross.