Pollution of the Guanabara Bay continues to be a concern for sailors as they prepare for the 2016 Summer Olympics in Rio de Janeiro.

According to The Associated Press, the Guanabara Bay is a familiar venue for sailors around the world, but untreated human waste has been tossed into the bay for decades. Rio de Janeiro and other nearby cities dump nearly 70 percent of their untreated sewage into the water. In May, Carlos Francisco Portinho, Rio de Janeiro's state environment secretary, wrote a letter to Sports Minister Aldo Rebelo saying that it will take more than a decade to lower the bay's pollution to a respectable level. 

"The sailors and boats do not want to be in a field of play where there is any type of objects," Alastair Fox, head of competitions at the International Sailing Federation, told BBC, adding that competing sailors have run into sofas, a door and a dead dog recently.

Olympics organizers have invited teams to test the water, AP reports. On Sunday, U.S. sailing officials had medical experts do so. Josh Adams, managing director of the U.S. Olympic sailing team, told AP that the waters were shown to "be contaminated," and unspecified "preventive measures" will be taken, but "nothing really alarming" was found.

"The tests were positive, and we can confirm that water is safe for the athletes," Julie Duffus, Rio 2016 sustainability manager, told BBC.

Adams thinks the water will be suitable for his team.

"We feel our sailors are safe, and we're aware of the issues with the water quality in Guanabara Bay," he said. "We know and have proven with our own water testing project that the water is contaminated, but we didn't discover anything that people didn't already know. It's contaminated largely because of unregulated sewage."

Still, some have their concerns. For example, Alain Sign, a British sailor, described the bay as "a bit darker than usual," with smells reminiscent of a "toiler" or "open sewer."

"Around the edges is the worst where it all collects," he said. "I wouldn't want to go paddle boarding and capsize."

Fox said the water testing showed "good" enough results for international standards and he would sail in it, but added that rain could still send more debris and sewage into the water.

"It wouldn't be a good test if it didn't rain," Fox said. "We need to see it when it's bad and when it's good. ... Ultimately we need to have a clear field of play. We can't have objects in that water that can affect racing."

Follow Scharon Harding on Twitter: @ScharHar.