2. Foul, disgusting, fetid water
You may or may not get bitten by a mosquito, but you're DEFINITELY going to come into contact with water. Lest you think that's too many vague adjectives to describe water quality, why don't you read what local biologist Mario Moscatelli told Public Radio International about Rio's mighty rivers:
"The rivers feeding into the lagoons are pure sh--... the feces of thousands of people emptied into the river without treatment."
Rio 2016: The Feces of Thousands of People Emptied Into the River Without Treatment. Could be a catchy slogan! The rest of the piece on Rio's water conditions is truly terrifying, replete with ominous phrases like "nausea, dizziness, vomiting, diarrhea" and "the water situation in Rio is dire." This comes in addition to the AP's reporting on the crisis, which essentially says the water Olympians will be using is pathogen-filled sewage. Don't worry TOO much, though -- there's a mere 99% chance of getting sick after ingesting three teaspoons of the stuff, so it'll take... ohhhh wait, no, that's really bad.