Research carried out by the associated press reported that there are high counts of active and infectious human adenoviruses in the waters of Guanabara Bay, Copacabana beach and the Rodrigo de Fritos Lake in Brazil.
The pollution is caused by the high amounts of raw sewage being disposed of in the water by the city. When the city of Rio d Janeiro offered to host the Olympic games of 2016, it promised to increase cleaning by 80%.
Until now, however, the cleaning is only up to 49% from the previous 17%. The viruses cause fever, diarrhea, vomiting and respiratory problems.
Some athletes have already reported being ill after being in the water.