Australian sailors continue to be hindered by rubbish days ahead of the Rio Olympics

— -- Three weeks out from competition, Australia's sailors are still running into rubbish and forced to stop their boats while training on Rio's Olympic courses.

While the raw sewage at Marina da Gloria has been cleaned up, out on Guanabara Bay defending 470 gold medallist Mat Belcher and his partner Will Ryan are still encountering obstacles ranging from dead animals to plastic bags.

"Two or three times a day we would be caught up with rubbish on our foil," Belcher told AAP from Rio.

"We need to stop, slow the boat down completely and raise our foils.

"It's getting better, hopefully we can get it down to one or two a week."

But, despite organisers' assurances, Belcher fears rubbish could play a dramatic role in the medal race.

"Yeah, absolutely that could happen," he said.

"What we've been told is they're going to clean the course prior to each day, they will go on course and ensure that won't happen."

Plastic bags almost cost Belcher and Ryan gold in a 2014 event in Rio when they dropped to last place in the medal race after being forced to stop and clear the rubbish off the boat.

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They caught up enough places to secure the points to win gold, but Belcher is aware it could have been disastrous.

"It had a massive, massive impact. Hopefully that doesn't happen in the Games," Belcher said.

In their nine trips to Rio in the past three years, Belcher and Ryan have hit a chair and an esky on the water as well as countless bag and cans, but have seen some improvement in water quality.

"It's not ideal," Belcher said.

"Inside the marina there's been a dramatic improvement, it's much more pleasant than having a raw sewage outlet where you launch your boat.

"But the water is still polluted and there's a lot of rubbish. We're hoping organisers can clean that up as we get closer to the Games.

"There's all sorts of rubbish - dead animals, furniture, plastic bags, a lot of coke cans.

"We've certainly heard a lot that they're going to do everything they can to make sure it's clean.

"We're happy with what they're trying to do."

Belcher teamed with Ryan after winning the 470 class gold medal with Malcolm Page at the London Games in 2012 and the new pair go to Rio as firm favourites after winning three of the past four world championships.