The carcasses of twaite shad - small silver fish belonging to the herring family - have filled huge areas of the Bay, about 12 miles from Marina da Glória, the start of the sailing competition. 

Some were even found washing up on the coastline outside Rio de Janeiro's international airport.

They were discovered by inspectors testing pollution in the Bay, which has consistently high levels of garbage and untreated sewage in the water.

Rio de Janeiro's environmental agency says it has launched an investigation, with results expected next month. 

Officials believe the fish fell victim to the intense drought which is currently affecting the city. 

The Government finally admitted last month it would miss its target of reducing water pollution by 80 per cent by the start of Rio 2016. 

The sailing venue has been beset by problems since Rio were awarded the Olympics and Paralympics six years ago, with local officials struggling to keep their promises to clean up the Bay.

The Bay covers a perimeter of 143 kilometres and has been heavily impacted by urbanisation, deforestation, and pollution of its waters with sewage, garbage and oil spills.

More than 70 per cent of the sewage from 12 million inhabitants of Rio de Janeiro flows into the Bay untreated.

In December environmental officials discovered a drug-resistant "super-bacteria" capable of causing a number of different infections.

The first Rio 2016 sailing test event was a success but most competitors complained about the smell and some reported seeing dead dogs in the water ©Getty Images

The first sailing test event last August was largely considered a success.

Some competitors, though, claimed they had seen dead dogs, cars, rats, furniture and a part of the wall during the competition and there had been a "nasty stench".

The venue is certain to come under intense scrutiny when this year's test event takes place there between August 8 and 18, featuring 380 athletes from 10 events. 

Nawal El Moutawakel, chair of the International Olympic Committee's Coordination Commission, which completed its eighth visit here yesterday, claimed they had received assurances from officials that the Bay will be safe to compete in during Rio 2016. 

"We want every single venue to be ready for the athletes to compete in a secure and safe manner," she said.

"We have been given reassurances that all the venues will meet the level...so athletes can compete."

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