British sailor Hannah Mills says the polluted waters of Rio de Janeiro could hinder her chances of winning gold in next year's Olympic Games.
Mills and Saskia Clark finished 2015 with victory in the 470 class at the Copa Brasil de Vela event at the Olympic sailing venue.
World Sailing says the water quality in Rio needs major improvement, and Mills admits it remains a significant worry.
"The rubbish is the big concern on some of the race courses," Mills said.
"If we're racing and we get rubbish stuck under our boats, that has a huge impact on your performance.
"It slows you down, you have to stop, lift up the foils and get the rubbish off and that's a major concern for us.
"Clearing the rubbish out of the water would certainly make a massive difference to competitors."
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A statement from the Rio 2016 organising committee earlier this month said the water at the sailing venue "meets the relevant standards".
However, tests at Guanabara Bay have revealed high levels of bacteria and viruses coming from human sewage.
Two sailors contracted infections at a test event in August, which they claim were caused by the waters.
World Sailing will conduct the latest site visit in late January to assess work being done to improve the quality.
Cardiff-born Mills, 27, and Clark, 36, from Colchester, won a silver medal at London 2012 and have already qualified for next year's Games.
They claimed a gold medal at the 2012 World Championships and silver in 2015 and are ranked number one in the world in the 470-class.
The Olympics begin on 5 August 2016.