RIO DE JANEIRO (AP) — Just days ahead of the Olympic Games the waterways of Rio de Janeiro are as filthy as ever, contaminated with raw human sewage teeming with dangerous viruses and bacteria, according to a 16-month-long study commissioned by The Associated Press.

Not only are some 1,400 athletes at risk of getting violently ill in water competitions, but the AP’s tests indicate that tourists also face potentially serious health risks on the golden beaches of Ipanema and Copacabana.

The AP’s survey of the aquatic Olympic and Paralympic venues has revealed consistent and dangerously high levels of viruses from the pollution, a major black eye on Rio’s Olympic project that set off alarm bells among sailors, rowers and open-water swimmers.

Since the AP released the initial results last July, athletes have been taking elaborate precautions to prevent illnesses that could potentially knock them out of the competition, including preventatively taking antibiotics, bleaching oars and donning plastic suits and gloves in a bid to limit contact with the water.

But antibiotics combat bacterial infections, not viruses. And the AP investigation found that infectious adenovirus readings — tested with cell cultures and verified with molecular biology protocols — turned up at nearly 90 percent of the test sites over 16 months of testing.

“That’s a very, very, very high percentage,” said Dr. Valerie Harwood, Chair of the Department of Integrative Biology at the University of South Florida. “Seeing that level of human pathogenic virus is pretty much unheard of in surface waters in the U.S. You would never, ever see these levels because we treat our waste water. You just would not see this.”

While athletes take precautions, what about the 300,000-500,000 foreigners expected to descend on Rio for the Olympics? Testing at several of the city’s world-famous beaches has shown that in addition to persistently high viral loads, the beaches often have levels of bacterial markers for sewage pollution that would be cause for concern abroad — and sometimes even exceed Rio state’s lax water safety standards.

In light of the AP’s findings, Harwood had one piece of advice for travelers to Rio: “Don’t put your head under water.”

Danger is lurking even in the sand. Samples from the golden beaches at Copacabana and Ipanema revealed high levels of viruses, which recent studies have suggested can pose health risks — particularly to babies and small children.

“You know how quickly an infant can get dehydrated and have to go to the hospital,” said Harwood. “That’s the scariest point to me.”

While local authorities including Rio Mayor Eduardo Paes have acknowledged the failure of the city’s water cleanup efforts, calling it a “lost chance” and a “shame,” Olympic officials continue to insist Rio’s waterways will be safe for athletes and visitors. The local organizing committee did not respond to multiple requests for comment, though it has previously said bacterial testing conducted by Rio state authorities has shown the aquatic venues to be within state guidelines.

The crux of the issue lies in the different types of testing used to determine the health and safety of recreational waters.

Bacterial tests measure levels of coliforms — different types of bacteria that tend not to cause illnesses themselves but are indicators of the presence of other, potentially harmful sewage-borne pathogens such as other bacteria, viruses and protozoa that can cause cholera, dysentery, hepatitis A and typhoid, among other diseases. Bacterial tests are the worldwide standard because they’re cheap and easy.

But there’s a growing consensus that they’re not ideal for all climates, as bacteria break down quickly in tropical weather and salty marine waters. In contrast, viruses have been shown to survive for weeks, months or even years — meaning that in tropical Rio low bacterial markers can be completely out of step with high virus levels.

That disparity was borne out in the AP’s testing. For instance, in June 2016, the levels of fecal coliforms in water samples at Ipanema Beach were extremely low, with just 85 fecal coliforms per 100 milliliters. But still, it had high readings for rotavirus, the main cause of gastroenteritis globally, with 32.7 million rotaviruses per liter.

The testing revealed alarming spikes in fecal coliform levels — the very measure the state government uses to determine the safety of Rio’s recreational waters.

“If these were the reported values in the United States, let’s say in California, there is definitely an indication of a problem,” said Dr. Kristina Mena, a waterborne virus expert at The University of Texas Health Science Center at Houston.

According to California’s bacterial tests standards, 400 fecal coliforms per 100 milliliters is the upper limit for a beach to be considered safe for swimming. AP’s tests revealed that Copacabana Beach, where the marathon and triathlon swimming are to be held and thousands of tourists are likely to take a dip, exceeded California’s limit five times over 13 months of testing.

The beaches even violate Rio state’s own standards, which are much less stringent than those in California, many other U.S. states and beach-loving countries such as Australia and New Zealand.

Promises to clean up Rio’s waterways stretch back decades, with a succession of governors setting firm dates for a cleanup and repeatedly pushing them back. In the city’s 2009 Olympic bid document, authorities pledged the games would “regenerate Rio’s magnificent waterways.”

Just over a month before the games, biologist Mario Moscatelli spent more than two hours flying over Rio in a helicopter.

Viewed from above, rivers are tar-black; the lagoons near the Olympic Park bloom with fluorescent green algae; surfers paddle amid a giant brown stain that contrasts with the azure of the surrounding waters.

“The Guanabara Bay has been transformed into a latrine,” said Moscatelli, an activist who’s the most visible face of the fight to clean up Rio’s waterways. “Unfortunately Rio de Janeiro missed the opportunity, maybe the last big opportunity” to clean it up.

———

Associated Press writers Peter Prengaman, Stephen Wade and Diarlei Rodrigues contributed to this report.

———

Peter Prengaman on Twitter: twitter.com/peterprengaman