RIO DE JANEIRO (AP) — With 500 days to go until the start of the 2016 Olympics in Rio de Janeiro, the head of the local organizing committee pledged Tuesday that the games would be the motor of the biggest urban transformation of any Olympic city.

Carlos Nuzman's comments came a day after Rio's mayor added his voice to the chorus of public officials who've expressed doubts about the completion of a promised cleanup of the city's sewage- and trash-filled waterways, which has been touted as an enduring legacy of the games.

Speaking at a news conference, Nuzman brushed aside repeated questions about the stalled cleanup of Rio's blighted Guanabara Bay, where the Olympic sailing events are to be held, insisting that routes would be up to snuff for the competition. In their bid, Brazilian officials had pledged to slash the amount of raw sewage flowing into the bay, which is so polluted it stinks and its once-crystalline beaches are off-limits for swimming.

Nuzman hailed Rio's urban mobility projects, as well as the ongoing renovation of the city's derelict port region, saying they would help forge a Rio before the games and a Rio after the games. He also insisted the Olympic infrastructure projects were on schedule and under budget.

Rio's Olympic project has come under fire from activists of all ilk, from environmentalists furious about the failed water cleanup and the construction of the Olympic golf course inside a nature preserve, to others angry about the forced evictions of slum dwellers to make way for new expressways and residential towers. Some critics contend aspects of Rio's Olympic project are aimed more at enriching real estate developers than promoting the public good in a city beset by violence, snarled traffic and social inequality.

Nuzman countered the criticism by saying that Rio would emerge from the games more changed even than Barcelona, the 1992 host city, or 1964 host city Tokyo.

"Rio will be the Olympic city with the greatest transformation," he said, adding that the people "are the ones who will get the most out of" the games.

Asked how this urban transformation would be measured and compared with that of prior host cities, Nuzman responded that it was self-evident.

"It's very clear, and it's the opinion of many people," he said. "Rio's a completely new city, completely different."

He insisted that the waters of Guanabara Bay would be safe for the athletes, who have been sounding alarm bells about possible health and safety hazards. Many sailors have voiced concerns about possibly falling ill from the spray of the fetid waters or potentially catastrophic crashes with floating garbage.

"They (the state government) are doing it, giving their best, making the effort" to clean up the bay, Nuzman said.

That contrasted with comments Rio Mayor Eduardo Paes made a day earlier in an interview with SporTV, where he said it was a "shame" the Olympic cleanup promise wouldn't be met.

"It is indeed a wasted opportunity," Paes added.

Without a well-developed sewage collection and treatment system or reliable garbage collection in the sprawling urban area that rings the bay, tons of garbage and raw sewage flow into the bay, as well as other area waterways — including Rio's world famous beaches.

In Rio's Olympic bid, authorities promised a massive cleanup. But as the Olympics have drawn nearer with little evidence of progress, the fetid bay has become a hot-button issue ahead of the Rio Olympics.

"Our expectations and trust are that we will have the bay and its waters ready to host the athletes from the entire world," Nuzman said.

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