"The reason for the unusual water color observed during the Rio 2016 diving competitions is that the water tanks ran out some of the chemicals used in the water treatment process," they said.
"As a result the pH level of the water was outside the usual range, causing the discoloration. The FINA Sport Medicine Committee conducted tests on the water quality and concluded that there was no risk to the health and safety of the athletes, and no reason for the competition to be affected."
The divers might disagree. In fact, a number of them were pretty disconcerted, if not distracted, by the color. “It (was) so green,” British diver Tonia Couch said. “As the sun went down it looked worse.”
An expert from the Pool Water Treatment Advisory Group (PWTAG), Ralph Riley, told USA Today that “if it has gone green and that is because there is not enough disinfectant there would be some kind of implied risk." Riley added PWTAG strongly advised against swimming in green water.