RIO DE JANEIRO (AP) — Athletes in next year's Summer Olympics here will be swimming and boating in waters so contaminated with human feces that they risk becoming violently ill and unable to compete in the games, an Associated Press investigation has found.

An AP analysis of water quality revealed dangerously high levels of viruses and bacteria from human sewage in Olympic and Paralympic venues — results that alarmed international experts and dismayed competitors training in Rio, some of whom have already fallen ill with fevers, vomiting and diarrhea.

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The AP commissioned four rounds of testing in each of those three Olympic water venues, and also in the surf off Ipanema Beach, which is popular with tourists but where no events will be held. Thirty-seven samples were checked for three types of human adenovirus, as well as rotavirus, enterovirus and fecal coliforms.

The AP viral testing, which will continue in the coming year, found not one water venue safe for swimming or boating, according to global water experts.

Instead, the test results found high counts of active and infectious human adenoviruses, which multiply in the intestinal and respiratory tracts of people. These are viruses that are known to cause respiratory and digestive illnesses, including explosive diarrhea and vomiting, but can also lead to more serious heart, brain and other diseases.

The concentrations of the viruses in all tests were roughly equivalent to that seen in raw sewage — even at one of the least-polluted areas tested, the Copacabana Beach, where marathon and triathlon swimming will take place and where many of the expected 350,000 foreign tourists may take a dip.