By Brenda Goh

RIO DE JANEIRO (Reuters) - Olympic organizers canceled diving training on Friday morning and shut the pool in an attempt to restore the water to its original blue color, three days after its emerald hue stirred concern among competitors.

The pool turned green on Tuesday, becoming the subject of numerous jokes and creating a headache for organizers. An adjacent pool used for water polo and synchronized swimming has also started to change color.

Despite promises to restore the color of the pool at the Maria Lenk Aquatic center by Wednesday evening, organizers were still trying to adjust its chemical levels, a spokesman for Rio 2016 told a news conference.

"We have learnt that chemistry is not an exact science. Some things, as you can see, have gone on longer than expected," Mario Andrada said.

Competitors were performing dry training in the venue on Friday, using an area where divers can practise using trampolines, platforms and harnesses.

The organizers said the pool would reopen later on Friday for training as well as for the women's individual three-meter springboard preliminaries.

World swimming governing body FINA said the color change was the result of a failure by the organizers to sufficiently treat the water after tanks at the venue ran out of chemicals.

The organizers responded by putting more chlorine, a chemical that kills algae and helps to keep water blue, in the pool and its neighbor but water polo players later complained about stinging eyes.

"This was because our first reaction to the water turning green was to use more chemicals," Andrada said. "We reduced immediately the quantity (of chlorine)."

Andrada said the discolored water posed no health threat to competitors and was being regularly tested by health experts from the International Olympic Committee (IOC), FINA and Rio 2016.

Heavy rain in recent days had made it more difficult to fine-tune the levels of chlorine in the open-air pool accurately, he added.

(Reporting by Brenda Goh and Daniel Flynn; Editing by Clare Fallon and Meredith Mazzilli)