During Tuesday night's diving final at the Rio Olympics something baffled us all - and it wasn't just how is it humanly possible to do a double-tuck, triple-bend twisting pike.
The pool, instead of its usual azure blue, resembled green jelly and appeared to get greener by the hour.
Everyone was baffled.
Especially Tom Daley.
Organisers have said that there was no risk to the athletes and they are investigating why it happened.
But that hasn't stopped others putting forward their own theories.
One theory suggests that the chlorine levels were wrong. Combine that with the pool's temperature, which is a friendly environment for microbes to grow in, then you have a algae filled pool.
When copper oxidises it turns green - perhaps there is a pipe corroding in the pool's waterworks?
The athletes requested the change
According to the BBC Pedro Adrega, head of communications at Fina, swimming's governing body, suggested that the athletes had perhaps asked for the colour change to lessen the effect of the sun's glare.
While it is unlikely to be wee - you'd need a lot of wee - some have suggested that the pool has become contaminated by pollution.
Some even suggested that the entire pool has been used for drug testing...