RIO DE JANEIRO (AFP) - Officials at the Rio Games diving competition were scratching their heads Tuesday over the colour of the pool water, which had turned an odd green colour overnight.

The women's 10m synchronised platform competition took place with athletes plunging into a murky green diving well that contrasted sharply with the normal light-blue of the adjacent water-polo pool.

Olympic officials said they were investigating the cause.

"Water tests at Maria Lenk Aquatics Centre's diving pool were conducted and there was found to be no risk whatsoever to athlete's health," said Simon Langford, the venue's media manager.

"We are investigating to determine what the cause of the situation was, but we are happy to report that the competition was successfully concluded."

He declined further comment.

Brazil's hosting of the games already has seen a number of organisational snafus including flawed Chinese flags at official ceremonies, complaints about huge queues, Olympics transport chaos and a wave of thefts.

British diving star Tom Daley, who won bronze in the men's 10m synchro on Monday, tweeted a photo of the aquatics centre scene, with the difference between the two pools clearly visible.

"Ermmm... what happened?!" he added.

But competitors in Tuesday's event shrugged it off, saying it had no impact on them or their performances.

"I thinks pretty normal for an outdoor pool, so it wasn't a big deal for us," said Pandelela Rinong, who won silver for Malaysia along with Cheong Jun Hoong.

The water had been a normal colour on the first two days of diving.