If “brain-eating amoebae” isn't the most terrifying combination of words you’ve ever heard, it will be by the time you finish reading this article. Although infection from the Naegleria fowleri amoeba is rare, it does happen from time to time. Just last month, a 29-year-old man died from a brain-eating amoeba after visiting a wave pool in Waco, Texas. The CDC is currently investigating the incident. Here are a few things you should know about this pernicious organism.

1. THEY LIVE IN WARM FRESH WATER.

Warm bodies of fresh water like lakes, rivers, and hot springs are usually where the single-celled amoebae like to hang out. They can also be found in soil, and in extremely rare cases, in contaminated tap water or swimming pools that haven’t been properly chlorinated. While most people encounter the amoebae in lakes or rivers, the CDC reports found that between 2007 and 2016, one person became infected after using a backyard slip-n-slide and three people became infected after using a nose irrigation device. Contaminated tap water was to blame in all four cases.

2. YOU WON’T GET INFECTED FROM SWALLOWING CONTAMINATED WATER, THOUGH.

Infection only occurs when water containing Naegleria fowleri enters the nose. In other words, accidentally swallowing river water while swimming doesn’t put someone at risk, but getting water up one’s nose does. Although the presence of Naegleria fowleri in fresh water is common, infections still remain rare.

3. THEY’RE NOT USUALLY ATTRACTED TO HUMANS.

These amoebae don’t go out of their way to feast on human brains. In fact, they’re usually content to eat bacteria found in the soil or sediment of lakes or rivers. “Normally, it’s totally harmless, doing its own thing in the mud, eating whatever it finds there, going about its business, not bugging anybody,” biologist Dan Riskin told Mental Floss in 2017. However, once it enters a new environment (such as an unsuspecting victim’s nasal cavity), it resumes eating whatever it can find.

4. AFTER ENTERING THE NOSE, THEY TRAVEL UP THE OLFACTORY NERVE.

Once inside the nasal cavity, an amoeba starts eating away at the olfactory bulbs, which are responsible for processing information about odors. “It makes its way up that olfactory nerve, reproducing and eating, until it hits the brain,” Riskin said. “And once it’s in the brain, it’s game over for the kid that had it shoved up his nose.” That’s because the amoebae eat brain tissue and cells, resulting in brain swelling, necrosis, and usually death.

5. THE DISEASE IT CAUSES IN HUMANS IS ALMOST ALWAYS FATAL.

Once infected, a disease called primary amebic meningoencephalitis (PAM) sets in. Early symptoms include severe headache, fever, nausea, and vomiting, and some of the stage-two symptoms are seizures, hallucinations, altered mental state, and coma. Generally, people start to show symptoms about five days after infection and die five days after that. The fatality rate is more than 97 percent, but again, infection is rare. Of the 143 cases of infection reported between 1962 and 2017, only four people survived, according to the CDC. But don't worry, your odds of contracting a brain-eating amoeba are about 1 in 70 million.

6. YOU CAN REDUCE YOUR RISK BY PLUGGING YOUR NOSE.

Brain-eating amoebae shouldn't be at the top of your list of concerns while swimming—drowning, for instance, is a far greater danger—but there are still a few things you can do to protect yourself. Try squeezing your nose shut while jumping or diving, or keep your head above water while taking a dip.