Trash-free water at the Rio Olympics is not guaranteed but sailing competitors can at least expect a "fair" tournament, a top official said Wednesday.

Barely two weeks from the start of the Games, the Brazilian hosts are scrambling to reassure competitors that the bay staging the sailing and windsurfing contests will not be affected by massive pollution.

The concern is that fast, light boats or a windsurfer could run into floating garbage or even just snag a plastic bag, getting slowed down or knocked out of the race. There are also worries about bacteria in the sewage-laden waters.

Andre Correa, the Rio state secretary for the environment, showed off one of the new barriers aiming at preventing the flow of garbage into the bay and said he thinks competitors won't have trouble.

"A guy trains for 10 years, comes here and then hits a rubbish bag -- it would be terrible for him," Correa said.

"There is no bay in the world with no rubbish. Is there a chance we'll have some problem? There is a very small chance, but it can't be ignored. It's not impossible. But I am very optimistic that we can guarantee a fair regatta," he said.

Correa said the barriers, placed across 17 principal rivers, aim to stop 85 percent of garbage that used to run freely into the bay.

Regular boaters and clean-up crews on Guanabara report finding everything from dead animals to floating televisions and refrigerators, in addition to masses of plastic bottles and bags.

- Germs not trash -

The so-called eco-barriers on the rivers are having a huge effect, Correa said. Before the latest seven went into service, a network of 10 barriers had already stopped about 2,400 tons of rubbish over six months.

Cleaning up what Brazilian researchers have identified as drug-resistant super-bacteria and other potential health risks is much harder. An estimated half of the sewage emitted by the roughly nine million people living around Guanabara Bay is not treated.

Just in Rio's Duque de Caxias area, where the environment secretary was inspecting the eco-barrier, there is a population of about one million and none of their sewage is treated.

Even at the eco-barrier the stench rising from the fetid, trash-strewn water was intense. Next door, the poorly constructed wooden houses of a shantytown each had plastic sewage pipes leading directly into the river.

Correa insisted that strong currents in the bay mean that the sailing areas are clean enough for swimming, even if other areas are filthy. "Water quality has never been a worry of mine for the Olympics," he said.

Only the raw sewage that until recently was gushing into the marina where the sailing boats start posed a risk, he said, and that has been addressed. "For the last month the water quality has been good," he said.

In their winning bid to host the Olympics, Rio de Janeiro officials had promised to reduce pollution by 80 percent, a vow Correa described as absurd.

"It was badly done and added to the discrediting" of the local authorities, he said. "Today... no one believes them."

According to Correa, it would take another 25 to 30 years to clean up Guanabara -- if the state had what he said was the necessary 20 billion reais ($6.1 billion) in funding.

And "the government doesn't have 20 billion," he said.