Rio 2016 Olympic mascot Vinicius is seen on the top of the Sugarloaf cable car to mark 500 days to go until the Opening Ceremony of the 2016 Olympic Games in Rio de Janeiro, in this handout photograph released on March 24. [Photo / REUTERS]

Brazilian Olympic officials changed tack on March 24 and said they would only clean up lanes for sailors in 2016 and not the whole body of water for the sailing competition as originally promised.

Rio de Janeiro pledged to reduce pollution in the Guanabara Bay by 80 percent but officials have now confirmed that the target will not be reached.

"The area of competition for the Olympic Games will be ready," Carlos Nuzman, head of the Brazilian Olympic Committee, said at a press event to mark 500 days until the starting gun.

"Our obligation is to deliver the area for competing during the Games," he added.

His comments came 24 hours after the city's mayor expressed his disappointment at the broken promise.

"I think it is a lost opportunity, yes," Eduardo Paes told Sportv in an interview. "Not for the Olympics but for Rio, it’s important to Rio. De-polluting the Guanabara Bay is something we should have done.

"It’s a shame that the Olympics were not the reason or the motive, as in Sydney, to resolve the issue once and for all."

However, Paes said he did not believe the dirty waters would pose a risk for sailors.

The sailing events will take place in a relatively clean part of the bay and. as it is the dry season, there will be less water flowing into the bay from the five rivers that surround it, he said.

In addition, staff will be employed to keep flotsam and jetsam away from the boats.

The Rio state government recently withdrew so-called eco-boats that were dredging some of the worst rubbish from the waters.

Officials said they were reviewing the program and expected to announce new measures in the near future.

The cleaning of Guanabara Bay was a key part of Rio’s bid pledge and has long been a goal of successive local governments.

Hundreds of millions of dollars have already been spent but the water remains fetid, with Olympic sailors who visited the city for test events complaining of floating sofas and animal carcasses in the water.

When it bid to host the Games, Rio said it would cut the amount of raw sewage flowing into the bay by 80 percent but has since admitted that is unlikely.

Biologists last year said rivers leading into the bay contained a superbacteria that is resistant to antibiotics and can cause urinary, gastrointestinal and pulmonary infections.