Sewage pollution has long been a problem for Rio de Janeiro, and officials promised they would use the 2016 Summer Olympics as the springboard to finally clean up this stunningly beautiful city's waterways.

An Associated Press investigation shows that not only have they failed to do that, but that the waters are rife with illness-inducing viruses.

The AP teamed up with a noted Brazilian virologist to test water at three sites where Olympic and Paralympic athletes will compete, and also at one of Rio's most popular tourist beaches.

Since March, Fernando Spilki, coordinator of the environmental quality program at Feevale University, has conducted four rounds of tests. In each round, he's taken water samples from:

— Two points at the Marina da Gloria, the jumping-off spot for sailing events.

— Two points at the Rodrigo de Freitas Lake, near the start and finish lines of the rowing and canoeing competitions.

— One point on Copacabana Beach, where marathon and triathlon swimming takes place.

— One point on Ipanema Beach, where many of the expected 350,000 foreign tourists will take a dip.

Spilki tested for three types of human adenovirus, rotavirus, and enterovirus.

He also tested for bacterial fecal coliforms, used by most nations as the guide for determining whether recreational water is safe because the tests have long been cheap and easy to carry out.

Despite that, water quality experts say it's actually viruses that cause most waterborne diseases — and that there is little correlation between the numbers of viruses from human sewage in water to the bacteria found.

That was in large part what the AP found in Rio.

For instance, the water off Copacabana Beach where marathon and triathlon swimming will take place consistently had low fecal coliform counts. Yet counts there for two types of human illness-inducing adenovirus ranged from 2 million to 49 million per liter.

For scientists who monitor water in the U.S., any recreational bodies of water with counts of 1,000 human adenovirus per liter would set off alarm bells, prompting investigations into the cause of the pollution and possibly closing the beach.

The Olympic lake saw a range of adenovirus counts from nearly 14 million per liter to 1.7 billion per liter. The Marina da Gloria's readings were 4.3 million per liter on the low end to 533 million on the high end. At a popular spot on Ipanema Beach, those adenovirus counts were between 5 million per liter and 14 million per liter.

The AP will continue testing the waters through the 2016 Olympic games.