We finally have an explanation.

It was hard to miss when two of the Olympic swimming pools turned emerald green, and everyone - including Olympic swimmer Tom Daley- wanted to know why. https://twitter.com/TomDaley1994/status/763089368022192129?ref_src=twsrc%5Etfw While there were assumptions and guesses as to what made the water change colour - and things seemed to take a turn for the worst over the weekend - Olympic Officials have finally come out and explained the real reason. Gustavo Nascimento, director of venue management for Rio 2016, said hydrogen peroxide was the cause. A contractor allegedly mistakenly dumped 160 litres of hydrogen peroxide into the pools late last week which caused an adverse reaction when it mixed with chlorine. Hydrogen peroxide can be used to clean the pools but it is not meant to be combined with chlorine as the chemical reaction causes a colour change. It also caused organisms to grow in the water, which included algae. Organisers have said that they will drain the water polo pool only, as a full 10 hours is needed to drain and refill the pool. The diving pool which caused some divers to report having itchy eyes will remain as it is for now, though organisers are continuing to treat the water in attempts to restore the original colour. Ithcy eyes wasn't the only complaint about the pools, as other athletes are also complaining about the awful smell coming from the emerald water.