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 has set off alarm bells among sailors, rowers and open-water swimmers.

In light of the findings, biomedical expert Dr. Valerie Harwood had one piece of advice for travelers to Rio: “Don't put your head under water.”

The most contaminated points are the Rodrigo de Freitas Lagoon, where Olympic rowing will take place, and the Gloria Marina, the starting point for the sailing races.

Sampling at the Lagoon in March 2015 revealed an astounding 1.73 billion adenoviruses per liter. By this June, adenovirus readings were lower but still hair-raising, at 248 million adenoviruses per liter. By comparison, in California, viral readings in the thousands per liter set off alarm bells.

Despite a project aimed at preventing raw sewage from flowing into the Gloria Marina through storm drains, the waters remain just as contaminated. The first sampling there, in March 2015, showed over 26 million adenoviruses per liter. This June, over 37 million adenoviruses per liter were detected.

The first results of the AP study published over a year ago showed viral levels at up to 1.7 million times what would be considered worrisome in the United States or Europe. At those concentrations, swimmers and athletes who ingest just three teaspoons of water are almost certain to be infected with viruses that can cause stomach and respiratory illnesses and more rarely heart and brain inflammation — although whether they actually fall ill depends on a series of factors, including the strength of the individual's immune system.

Since the AP released the initial results in July 2015, athletes have been taking elaborate precautions to prevent illnesses that could 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 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.”

Phelps, Ledecky set for relays: Maryland natives Michael Phelps and Katie Ledecky have been named to the U.S. 4x100-meter freestyle relay teams, according to USA Today.

Neither swimmer qualified for the race at the U.S. Olympic trials a month ago. Phelps is set to compete in three individual events — the 100 and 200 butterfly and 200 individual medley — while Ledecky is the favorite in her three — the 200, 400 and 800 freestyle.

The relay lineups do not have to be submitted until the night before Sunday's race. Both U.S. relay teams are likely to finish in the top three, which would give Phelps and Ledecky their first medals of the games.

Doping-scandal sniping: The split between Olympic leaders and global anti-doping officials over the Russian doping scandal continues to escalate.

The World Anti-Doping Agency fired back Monday, a day after International Olympic Committee president Thomas Bach suggested the agency was to blame for the last-minute chaos over the participation of Russian athletes in the Rio Games.

Bach said the agency should have acted sooner on evidence of state-sponsored doping rather than release the damning report by Canadian investigator Richard McLaren so close to the games, which open Friday.

“While it is destabilizing in the lead-up to the games, it is obvious, given the seriousness of the revelations that [McLaren] uncovered, that they had to be published and acted upon without delay,” WADA president Craig Reedie, who is also an IOC vice president, said in a statement Monday.

On Sunday, Bach defended the IOC's decision not to ban the entire Russian delegation from the Olympics, and said the IOC was not responsible for the timing of the latest WADA report, which came out July 18.