Had someone put coloring in the water? Was their TV set broken?
Eventually some answers came. There had been a change in alkalinity in the water, said one official. Another blamed algae.
The green diving pool at Maria Lenk Aquatics Centre next to another that is the usual color - although that too later turned green
Meanwhile, FINA, the international governing body for swimming, said the water tanks had run out of water-cleaning chemicals.
With so many different answers, it's about as clear as the water in the murky pools.
