Patrick Hausding (GER) of Germany swims in the green coloured water of the diving pool at the Maria Lenk Aquatics Centre.
In picture: Patrick Hausding (GER) of Germany swims in the green coloured water of the diving pool at the Maria Lenk Aquatics Centre.Reuters

The mystery of at least two simming pools turning green from the usual blue and smelling like farts seems to have been solved, with contractors being blamed for dumping too much hydrogen peroxide (H2O2) into the water. The Olympic organisers have admitted that contractors had dumped at least 160 litres of hydrogen peroxide into the waters of the pools at the Rio aquatic centre. 

The contractors are now being accused of dumping 80 litres of hydrogen peroxide each into the waters of two pools on Friday, Aug. 5, before the games began. The result of that was that one of the pools on Tuesday, Aug. 9, turned a shade of green that has been described as "emerald" by many. The second pool followed suit soon after.

The pools are said to have turned green because the hydrogen peroxide, which is often used as a disinfectant in a diluted form, neutralised the chlorine in the waters of the pools, which helped algae proliferate in them. It was these algae that imparted the pools their green colour.

Swimmers who practised or participated in events of these pools have complained of itchiness in their eyes and an overall reduction of visibility due to the murkiness of the waters. It did not help that the chlorine was absent, as it led to more micro-organisms being added to the water as around 120 athletes used the pools. 

However, it's not as if the hydrogen peroxide was not supposed to have been put in the pools. Rio 2016 Venue Management Director Gustavo Nascimento said: "This is a way of cleaning swimming pools, but you're not supposed to combine it with chlorine." 

The pools were expected to host a synchronised swimming event on Sunday, before which the water would be drained and fresh water put in. 

What is hydrogen peroxide?

Hydrogen peroxide (H2O2) is a chemical compund that is used, among other things, as a disinfectant, oxidiser and bleaching agent, but rarely in its purest, most concentrated form. Whenever it is used, it is first diluted with water, which changes its properties drastically. 

For example, pure hydrogen peroxide can cause extreme burns if it comes into contact with the human tissue, and has been known to burn other things on contact. However, in its diluted form, it is known to be used in a lot of ways that are beneficial for human beings, like those mentioned above. 

Hydrogen peroxide is also often known as a compound that is "one oxygen away from water," given their chemical formulae. Water is H2O. However, the drastic differences in their behaviour has been noted by chemists for many years, and also led to jokes such as this one:

Two scientists walk into a bar. 

The bartender asks them for their order.

Scientist 1: "I'll have some H2O."

Scientist 2: "I'll have some H2O, too."

Scientist 2 dies.