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Athletes have been dismissing the dangers of swimming in Rio de Janeiro's dirty waters, saying the risks are not great enough to alter their Olympic plans.

Despite a warning from a state environmental agency that some Olympic venues are unsafe, triathletes and paratriathletes entered the waters off Copacabana Beach Friday in an area considered "unfit" for swimming.

They'll continue to compete this weekend in test events for next year's games.

"We know we are exposed to viruses, maybe to health problems later," Costa Rican triathlete Leonardo Chacon said.

"But in my case, I have invested so much to prepare myself for this and I want this to happen because I can't recuperate this investment any other way other than competing and winning the points that I need to win."

Brazil prepares for Rio 2016

For many, the reason is simple. There will be spots available for the 2016 Olympics in Sunday's triathlon test event in Rio. And the test events provide a unique opportunity to get to know the environment.

"For me, the greater risk would be not knowing the course," said American paratriathlete Patricia Walsh, who was getting familiarised with the venue that will be used in paratriathlon's debut in the games next year.

"For any athlete, getting in the water, any water, has its own amount of risk. If I didn't do that, I think it would be a greater risk than going in the water."

The Rio de Janeiro environmental agency said the water was declared unfit based on the results of a Monday water test.

The same spot, which is near where triathletes began swimming, has been declared unfit 10 previous times this year alone.

Extreme water pollution is common in Brazil, where the majority of sewage is not treated. Raw waste runs through open-air ditches to streams and rivers that feed the Olympic water sites.

Although most athletes have been downplaying the dangers of swimming on Copacabana Beach, some teams have taken precautionary measures.

Italian team doctor Stefano Righetti said athletes went through probiotic therapy to protect them against some of the diseases they could get by going into the water.

Source: Reuters