RIO DE JANEIRO (AP) — A drug-resistant “super bacteria” that’s normally found in hospitals and is notoriously difficult to treat has been discovered in the waters where Rio de Janeiro’s Olympic sailing events will be held, scientists said Monday.

The Instituto Oswaldo Cruz, Brazil’s most respected health research institute, said it has discovered bacteria that produce an enzyme that make it resistant to most forms of treatment in water samples taken from various spots along the Carioca River. Among the spots is where the river flows into the city’s Guanabara Bay, site of the 2016 sailing and wind surfing events.

Bacteria with the so-called KPC enzyme are difficult to treat. The institute said no instances of infection resulting from the contaminated water have yet been detected but warned of possible danger to swimmers.

“The illnesses caused by these microorganisms are the same as those caused by common bacteria, but they require stronger antibiotics and, sometimes, can require hospitalization,” the study’s coordinator, Ana Paula D’Alincourt Carvalho Assef, wrote in an email to The Associated Press. “Since the super bacteria are resistant to the most modern medications, doctors need to rely on drugs that are rarely used because they are toxic to the organism.”

Even if they don’t immediately fall ill, those who come into contact with the bacteria run the risk of becoming carriers of the microorganism, the institute said in its statement.