With just 17 months until the start of the 2016 Olympic Games, the level of sewage in the water at Rio's sailing venue is a major concern.

Several Olympic-medal winning sailors have said Guanabara Bay is the dirtiest place they have ever competed, citing incidents of dodging floating sofas, plastic bags and even dead animals.

Rio de Janeiro pollution
A sofa floats in the polluted waters of Jacarepagua Lagoon, during a press tour organised by biologist Mario MoscatelliRicardo Moraes/Reuters

Cleaning up the bay was a key promise of Rio de Janeiro's Olympic bid.

Organisers had set a target of cutting the amount of untreated sewage flowing into it by 80%. It is thought they are achieving around 48%.

Rio de Janeiro pollution
Bubbles appear on the surface of the polluted Jacarepagua LagoonRicardo Moraes/Reuters

Biologist Mario Moscatelli said games organisers are playing "Russian roulette" with competitors' health. "If, by chance, they pass through a contaminated area, and they are in contact with this water, it could develop into a problem. It could develop into a hepatitis or an intestinal problem," he said.

He also warned that if a boat capsized, an athlete could hit a sofa or other floating object at high speed.

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Biologist and ecologist Mario Moscatelli gives a press conference standing on a heap of rubbish alongside Guanabara BayChristophe Simon/AFP
Rio de Janeiro pollution
Pollution floats in Guanabara Bay, the sailing venue of the 2016 Olympic Games in Rio de JaneiroMario Tama/Getty Images

One of Britain's top sailors Nick Thompson, who is looking to be chosen for the Laser and emulate Ben Ainslie's 2000 Sydney gold in the single-handed dinghy, told Reuters he had been very sick at a Rio test regatta last year.

"Water quality is my biggest personal concern. If you are sick during the Games, it's game over," Thompson said, adding that he was "taking probiotic supplements and fish oil to strengthen the gut".

The International Olympic Committee (IOC) had been reassured by Brazilian authorities that the water would be clean and safe by the time of the Games. However, on 3 March it was reported locally that the rubbish collection boats on Guanabara Bay had been halted due to a lack of funding.

Rio de Janeiro pollution
Pigs search through rubbish on the banks of the Cunha canal, which flows into the highly polluted Guanabara Bay in Rio de JaneiroChristophe Simon/AFP
Rio de Janeiro pollution
A bird flies over rubbish in Guanabara Bay in Rio de JaneiroSergio Moraes/Reuters

In December a drug-resistant "super bacteria" normally found in hospitals was also discovered in the water around the bay.

In February, thousands of dead fish were found in Guanabara Bay. Fish die-offs are also common in Rio's Rodrigo de Freitas Lake, where the Olympic rowing competitions will be held.

Rio de Janeiro pollution
Dead fish float on the surface of Guanabara Bay in Rio de Janeiro on 24 February 2015Ricardo Moraes/Reuters
Rio de Janeiro pollution
Dead fish and rubbish float in the water of Guanabara BayRicardo Moraes/Reuters
Rio de Janeiro pollution
A dead fish lies next to a football in the colours of the Brazilian flag on the banks of Guanabara BayRicardo Moraes/Reuters
Rio de Janeiro pollution
Workers remove thousands of dead fish from Guanabara Bay in Rio de JaneiroChristophe Simon/AFP