RIO DE JANEIRO -- The Rodrigo de Freitas lagoon, with its glistening waters, is one of this tropical city's most picturesque spots. Just don't look too closely at those waters.

As Rio de Janeiro prepares to host the Summer Olympics in less than a year, concern remains that the site for rowing and canoeing competitions and venues for other aquatic events are polluted and dangerous to athletes.

Last week, four coaches and 11 members of the U.S. team came down with stomach illnesses at the World Junior Rowing Championships after competing in the lagoon.

U.S. Rowing CEO Glenn Merry said the affected team members fell ill throughout the weeklong competition, which makes it difficult to determine if the polluted water is to blame.

“Everyone was at the lake every day, everyone was eating at the same hotel every day, there may have been some variances in what they consumed or something else, but we know that the lake is polluted,” Merry said. “I feel like it’s irresponsible to put it all on one thing … I want to make sure we cleared those areas before we say definitively our sanitation protocol wasn’t working or that it was the lake.”

But Kathryn Ackerman, the U.S. team physician, has an idea about the culprit. "My personal feeling is, I think it's from the lake," she told The Associated Press.