Four days after one of the pools at Rio's Olympic venue mysteriously turned green, authorities finally have an answer.

Hydrogen Peroxide. Officials organizing the Games said a contractor had erroneously put 80 litres of Hydrogen Peroxide into the pool which neutralised the chlorine. Due to the absence of chlorine the water appears to have become a breeding ground for alga, turning the colour of the water emerald green.

Prior to Saturday, even the authorities had different versions as to the cause of the green water such as sunlight and lack of wind. A spokesperson even suggested chemistry wasn’t an ‘exact’ science.     

Theories ranged from urine to green dyes close to that of the colour of the Brazilian flag as the reason behind the emerald. Another bizarre theory concluded that the pool was Shrek’s water park.

Apart from the theories, the athletes complained of a foul smell not only inside the pool but the whole building.

The Olympic diving pool has been closed again because of water quality issues...a German diver says "the whole building smells like a fart"

— Tom Steinfort (@tomsteinfort) August 12, 2016
 

The organizers maintained that the green water was not a health hazard but had to be replaced for the competitors and judges need underwater visibility for the synchronized swimming event.

Officials said on Saturday that the pool would be drained and replaced with nearly a million gallons of clear water before the start of the synchronized swimming on Sunday, reports Xinhua.

"We are going to grab the water from the warm-up pool, drain the water out of the competition pool and insert the water from the warm-up pool into the competition pool," Rio 2016 director of venue management Gustavo Nascimento told reporters.

"This will be done overnight and we will start preparing the competition pool for synchronised swimming, which is due to start at 11am."

The pool, one of three at the venue, is being used for diving, synchronized swimming and water polo.

Rio 2016 spokesman Mario Andrada said tests showed that the green water did not pose a health risk to athletes but conceded it was nothing but untoward.

"Of course it is an embarrassment because we are hosting the Olympic Games," Andrada said. "It should be light blue, transparent. We could have done better in fixing it quickly. We learned a painful lesson the hard way," Andrada said.