RIO DE JANEIRO, BRAZIL — A “super bacteria” has been found on five beaches in Guanabara Bay in Rio de Janeiro, Brazil, where upcoming Olympic water events will take place.

Two unpublished studies obtained by Reuters showed the presence of carbapenem-resistant Enterobacteriaceae (CRE) in water samples collected from 2013 to 2014. CRE has been classified by the U.S. Centers for Disease Control as an urgent public health threat. The bacteria can kill up to half of patients who suffer bloodstream infections.

Experts believe the super bacteria entered the city’s waterways when sewage from local hospitals were channeled into the bay.

The five beaches infected include Copacabana, Ipanema, Leblon, Botafogo and Flamengo. Flamengo beach, where spectators will gather to watch Olympic sailors compete, had the super bacteria in 90 percent of samples. Ten percent of Copacabana’s samples had the microbes, while Ipanema and Leblon beaches — the most popular with tourists — had samples that tested positive 50 and 60 percent of the time, respectively.

A second study was conducted by the Brazilian federal government’s Oswaldo Cruz Foundation lab. Results of that study will be published this month by the American Society for Microbiology. That study found genes of super bacteria in the Rodrigo de Freitas lagoon in the heart of Rio, and in a river that empties into Guanabara Bay.

The city had promised to clean its waterways as part of its bid for the Olympics. City officials have told CNN that 51 percent of the city’s sewage has been treated, up from 11 percent, but still nowhere near the 80 percent promised.