Olympic organisers admit they have been left red faced over Rio's green pool.
Five days after noticing the water turn teal, embarrassed organisers have made the "radical" decision to drain a pool at the Maria Lenk Aquatics Center and refill it before the synchronised swimming starts on Sunday.
However officials claimed they were happy with the progress of the adjacent green diving pool at the venue, dubbed "The Swamp" by competitors.
Rio Games organising committee spokesman Mario Andrada said water from the venue's warm-up area would be pumped overnight into the murky main pool which had been used for water polo.
The nearby diving pool continued to be used for competition on Saturday despite athletes claiming the water was worse than ever.
"It's pretty gross," Australian diver Maddison Keeney said.
"It was probably the worst it has been today." Andrada said water in the main pool would be replaced because synchronised swimming competitors and judges needed to see underwater, unlike diving.
He insisted the competitors' health was not at risk but admitted it wasn't a good look.
"Of course it is an embarrassment," he said.
"But embarrassment does not last forever.
"We've learned a painful lesson.
"We have over promised and under delivered."
He said the colour change on Tuesday was due to 80 litres of hydrogen peroxide being mistakenly added to the pool by a local contractor on August 5.
A venue spokesman said that had affected the chlorine's ability to kill algae.
Asked if they had a Plan B, Andrada said: "We do but we always found Plan A is better than Plan B."
Andrada insisted biological tests had confirmed there was no health risk despite the presence of algae.
"I don't want to know what is in there," Keeney said.
"I have never seen anything like it before."
Officials started draining the pool on Saturday afternoon.
Morning training sessions were cancelled on Thursday to allow the water to be still for longer, officials hoping it would speed up the process of killing the algae.
Some athletes have complained of itchy or sore eyes.
German diver Stephan Feck also posted on Facebook a photo of himself near the pool, holding his nose.
"The whole venue smells like somebody has fart(ed)," he wrote.