Last week we mentioned the upmost importance of bringing your own water along on a hike, and at the very least, boil it before you drink. The amount of random and disturbing creatures lurking in our natural water sources is a tad bit alarming — not to mention the added cocktail of chemicals and further troubling unmentionables that find their way in everyday.

So, to further alarm you, here are six of the nastiest bacterias and parasites that might be floating along just when you decide to quench your thirst. (We were going to show you more but honestly couldn’t stomach it.)

Name: Giardia lamblia
Domain: Eukaryota
The transmitters: Cows, beavers, deer and sheep.
Its ultimate goal: To colonize and reproduce in the small intestine.
Why it’s nasty: That small intestine, by the way, is yours. While it’s there, Mr. lamblia causes giardiasis, which will give you flu-like symptoms, especially in the stomach region.

Name: Salmonella
Domain: Bacteria
The transmitters: Aquatic vertebrates, birds and reptiles.
Its ultimate goal: This bacteria has been known to stay alive for weeks in a dry environment. And if you put it in water, those weeks can easily turn into months.
Why it’s nasty: While there are various strains, ingesting it can cause typhoid fever, paratyphoid fever or the foodborne illness salmonellosis. Yeah, yeah we know these might sound more like things you’d catch playing Oregon Trail. Nevertheless, they didn’t have bottled water back then, and you do.

Name: Toxoplasma gondii
Domain: Eukaryota
The transmitters: Warm-blooded mammals, specifically domestic and wild cats.
Its ultimate goal: To invade cells and slowly replicate in the parasite’s form.
Why it’s nasty: Leads to Toxoplasmosis. While some say up to one third of the world’s population carries this infection, it has proved to only have truly fatal effects on fetuses.

Name: Escherichia coli (commonly goes by its street name, E. coli)
Domain: Bacteria
The transmitters: Various strains can be found in humans, pigs, sheep, goats, cattle, dogs and horses.
Its ultimate goal: To chillax in the lower intestine of warm-blooded organisms.
Why it’s nasty: While some strains are completely harmless, others can give you really serious bouts of food poisoning. And that’s never fun — especially in the wilderness.

Name: Cryptosporidium
Domain: Eukaryota
The transmitters: Humans, cattle, sheep and goats.
Its ultimate goal: To reproduce in the small intestines.
Why it’s nasty: Causes Cryptosporidiosis, or Crypto, which will give you an upset stomach, and is one of the most common waterborne diseases. While that sounds fairly minor, it could have you feeling not so hot for up to a month.

Name: Hookworm
Domain: Animalia
The transmitters: Infected mammals.
Its ultimate goal: This will also set up shop in the small intestines of a mammal, be it dog, cat or human.
Why it’s nasty: Once this parasite begins its work, you’ll experience flu-like symptoms. If left untreated, that can evolve into anemia and protein deficiency, including emaciation, cardiac failure and abdominal distension.

(Images via Wikimedia Commons)