Olympic sailors looking to compete in the 2016 Summer Games have voiced concerns over sewage-infested waters swamped with rubbish and human waste in Rio de Janeiro's Guanabara Bay, where the Olympic sailing and windsurfing events will take place.

Athletes have described having to dodge a deluge of rubbish including floating mattresses, car tyres, submerged sofas, dog carcasses and even human corpses, as former Olympian medallist Lars Grael claimed, when sailing in the water - five years after Brazil won its Olympic bid.

The Bay was condemned as a “dump” in March by Germany’s sailing team because of the garbage-filled waters, where they questioned how the sailing regattas would be organised there.

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Nico Delle Karth, an Austrian sailor told The New York Times the stench of sewage made him scared of putting his feet in it to launch his boat. “I’ve never seen anything like this before,” he said.

Shape Created with Sketch. In pictures: Guanabara Bay ahead of the 2016 Summer Olympics Show all 6 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. In pictures: Guanabara Bay ahead of the 2016 Summer Olympics 1/6 Guanabara Bay A dog sits along the shoreline of the polluted waters of Guanabara Bay Getty Images 2/6 Guanabara Bay Guanabara Bay is seen in a section littered with debris on June 19, 2012 Getty Images 3/6 Guanabara Bay Boats float along the shoreline of the polluted waters of Guanabara Bay Getty Images 4/6 Guanabara Bay Rubbish building up along the shores Getty Images 5/6 Guanabara Bay An abandoned drainage pipe sits on the edge of polluted Guanabara Bay Getty Images 6/6 Guanabara Bay Trash floats on a polluted water channel that flows into the Guanabara Bay on 15 March 2014 AP 1/6 Guanabara Bay A dog sits along the shoreline of the polluted waters of Guanabara Bay Getty Images 2/6 Guanabara Bay Guanabara Bay is seen in a section littered with debris on June 19, 2012 Getty Images 3/6 Guanabara Bay Boats float along the shoreline of the polluted waters of Guanabara Bay Getty Images 4/6 Guanabara Bay Rubbish building up along the shores Getty Images 5/6 Guanabara Bay An abandoned drainage pipe sits on the edge of polluted Guanabara Bay Getty Images 6/6 Guanabara Bay Trash floats on a polluted water channel that flows into the Guanabara Bay on 15 March 2014 AP

“It can get really disgusting, with dog carcasses in some places and the water turning brown from sewage contamination,” Thomas Low-Beer, a Brazilian Olympic hopeful who sails in the bay added.

The fears over the conditions in the water come after The Associated Press claimed to have obtained a letter from Rio's state environment secretary Carlos Francisco Portinho, where he told sports minister Aldo Rebelo that pollution flowing into the bay could be cut to "over 50 per cent" - well below the promised reduction of 80 per cent.

Nearly 70 per cent of Rio's sewage goes untreated into its waters, according to AP. Danish Olympian Allan Norregaard, a bronze medalist at the 2012 Olympics, said Guanabara was "the most polluted place I've ever been." Other sailors interviewed by the AP referred to it as an "open sewer."

State officials are now using rubbish boats to collect floating debris and officials contend criticism of Guanabara Bay is exaggerated. Carlos Portinho, an environmental official in Rio, said reversing pollution in the bay was a “long-term project" and while three small “ecoboats”currently correct rubbish, 20 or 30 might be operating by the Olympics.

But Alastair Fox, head of competitions for the international sailing federation, said the body is now likely to conduct its own independent water quality tests in a bid to reduce concerns among athletes

"If someone picks up a bag, or hits a sofa or something like that, then clearly that is going to affect them in the race," Mr Fox said.

"We've seen numbers from teams of the fecal content in the Guanabara Bay, which clearly are not safe," he added. "For us, that's a matter of concern. We've been assured again by the organisers that they are doing everything they can."

However, Mario Moscatelli, a biologist and outspoken environmentalist said retrieving floating rubbish would not address the problem of untreated sewage.

In an open letter to Brazilian President Dilma Rousseff, he asked for the "release of the funds needed to recover the environmental assets, which are being used in Rio as garbage dumps and latrines."

The International Olympic Committee has said it will not conduct its own testing.