The Associated Press has been doing an independent study of Rio’s water quality for the past 16 months as the city prepares to host the Olympics. The main takeaway is this:

That warning, issued to the AP by Valerie Harwood, chair of the Department of Integrative Biology at the University of South Florida, applies not only to the 1,400 athletes who will compete in sports that utilize Rio’s waterways but also to the 300,000 to 500,000 foreign visitors who are expected to descend on the city for the Games, because some of them will certainly want to visit Rio’s famous beaches. But the water at places such as Copacabana beach have shown consistently high levels of both bacteria (which can be dealt with using antibiotics) and adenoviruses (which cannot). So getting any of that in your mouth is probably going to be unpleasant.

Even the sand isn’t safe.

“Samples from the beaches at Copacabana and Ipanema revealed high levels of viruses, which recent studies have suggested can pose a health risk — particularly to babies and small children,” the AP’s Jenny Barchfield writes.

At issue is the sewage that is regularly dumped into Rio’s waters, a practice the AP says has been going on for “centuries.” City and national officials promised to clean up the water when bidding for the games with billions of dollars in sewage-treatment improvements, a pledge that apparently has gone unheeded:

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. In March, 2015, sampling at the Lagoon revealed an astounding 1.73 billion adenoviruses per liter; 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 are enough to set off alarm bells. …
In June, 2016, the levels of fecal coliforms in water samples from Copacabana and Ipanema Beaches were extremely low, with just 31 and 85 fecal coliforms per 100 milliliters, respectively. But still, both had alarming readings for rotavirus, the main cause of gastroenteritis globally, with 7.22 million rotaviruses per liter detected in the waters of Copacabana, while 32.7 million rotaviruses per liter were found in the waters of Ipanema Beach.

And if you’re traveling to Rio with plans to head for the beaches, don’t expect any notice that things might not be safe: According to the AP, water-quality warning signs, which once were posted at the city’s most prominent beaches, have been removed.