Giardia poop often looks watery, greasy, pale, or yellowish, and it may float because fat is not being absorbed well. It can smell foul and come with gas, cramps, nausea, and fatigue. You cannot confirm giardia by sight; a stool test is needed when symptoms fit.
What is giardia, and how do hikers get it?
Giardia is a tiny parasite that can live in untreated water and cause a gut infection called giardiasis.
On trail, the usual risk is swallowing water contaminated with poop from infected people or animals. That can happen from a creek, lake, spring, shallow well, or even a “clean-looking” alpine trickle. Clear water can still carry parasites. Cold water can still carry parasites. Fast-moving water can still carry parasites.
The CDC’s giardia overview says symptoms usually start 1 to 2 weeks after infection and can last 2 to 6 weeks. That timing matters. If you drank untreated water yesterday and feel sick today, giardia is possible but not the neatest fit. Food poisoning, norovirus, heat stress, or another waterborne bug may be more likely.
What does giardia poop look like?
It often looks loose, watery, greasy, pale, yellowish, or floating.
The classic trail story is not just “diarrhea.” It is diarrhea with a slick or oily look, a strong rotten smell, loud gas, belly cramps, and that drained feeling where a simple hill suddenly feels rude. Some people also notice stool that floats or is hard to flush, which can happen when fat is not absorbed normally.
Still, your eyes cannot diagnose giardia. Many gut infections can cause watery poop, weird colors, mucus, urgency, and bad smells. A clinician may ask for one or more stool samples because giardia does not always show up in every sample. The CDC’s giardia testing guidance explains that several samples collected over several days may be needed.
| What you notice | Can fit giardia? | What else can cause it? |
|---|---|---|
| Watery diarrhea | Yes | Viruses, bacteria, foodborne illness |
| Greasy, floating, foul-smelling stool | Yes | Other malabsorption problems |
| Blood in stool | Not typical | Other infection or bowel inflammation |
| Severe dehydration signs | Possible with diarrhea | Any bad stomach illness, heat illness |
How long after drinking untreated water do giardia symptoms start?
Symptoms usually start 1 to 2 weeks after you swallow the parasite.
That delay is one reason giardia messes with hikers’ heads. You may feel fine for days after a trip, unpack your gear, wash the socks that should be burned, and then get hit the next week. The timing can make it hard to connect symptoms to one sketchy water source.
Common symptoms listed by the CDC giardia symptoms page include diarrhea, gas, stomach cramps, nausea, dehydration, and greasy poop that can float. Some people have no symptoms but can still spread the parasite through stool.
- Typical start: 1 to 2 weeks after infection
- Typical duration: 2 to 6 weeks
- Most common symptom: diarrhea
- Trail clue: symptoms after untreated water plus greasy, foul-smelling stool
Can you have giardia without diarrhea?
Yes, but diarrhea is the most common symptom.
Some people get bloating, burps, cramps, nausea, fatigue, weight loss, or appetite changes without constant bathroom runs. Others have mild symptoms, then a few rough days, then another mild stretch. That stop-start pattern can trick you into thinking you are getting better, especially if you are still hiking, eating less, and blaming your stomach on trail food.
Do not rely on one symptom. Look at the pattern: untreated water exposure, delayed start, gas, cramps, greasy stool, and symptoms that keep hanging around. That combination deserves a call to a healthcare professional.
What should you do if you think you got giardia on trail?
Start with fluids, hygiene, and medical advice.
Do not try to tough-guy your way through days of diarrhea in the backcountry. Dehydration can hit fast when you are hiking, sweating, and losing fluid through your gut. If you are still on trail and symptoms are strong, shorten the day, rest in shade, replace fluids, and make a conservative plan to exit if you are not improving.
- Hydrate steadily. Sip treated water often. Use oral rehydration products if you carry them.
- Keep your hands clean. Wash with soap and water when possible, especially after bathroom stops and before eating.
- Stop sharing food and bottles. Giardia spreads when tiny amounts of infected stool reach another person’s mouth.
- Call a healthcare professional. Ask whether stool testing makes sense for your symptoms and timeline.
- Do not self-prescribe antibiotics or antiparasitic drugs. Treatment depends on testing, symptoms, medical history, and clinician judgment.
The CDC’s giardia treatment page says people with diarrhea or symptoms should discuss treatment options with a healthcare provider. Medication may not be needed for people who test positive but have no symptoms.
When to see a doctor
See a doctor if diarrhea is persistent, severe, bloody, or paired with dehydration.
Get medical help quickly if you cannot keep fluids down, feel faint, have confusion, have a high fever, notice blood in stool, or see signs of dehydration such as very little pee, dry mouth, dizziness, or racing heartbeat. Children, older adults, pregnant hikers, and people with weakened immune systems should be more cautious.
You should also contact a clinician if symptoms last more than several days after a backcountry trip, if you are losing weight, or if greasy diarrhea keeps returning. Tell them where you hiked, what water you drank, when symptoms started, and whether anyone in your group is sick too. Those details help narrow the list.
How do you prevent giardia when drinking backcountry water?
Treat every wild water source before it reaches your mouth.
The cleanest-looking stream on the map still runs through an animal’s bathroom. Your job is not to judge water by sparkle. Your job is to treat it every time.
The CDC’s water treatment guidance for hiking and camping says boiling is the best way to kill giardia and other germs: boil water for 1 minute, or 3 minutes above 6,500 feet [1,981 m]. It also recommends filters certified for “cyst” and “oocyst” reduction or NSF Standards 53 or 58 when filtering for parasites.
- Filter water from lakes, rivers, springs, ponds, streams, and shallow wells.
- Keep dirty water away from bottle threads, caps, bite valves, and clean bags.
- Use treated water for brushing teeth.
- Wash hands after pooping and before handling snacks.
- Pack out toilet paper and bury poop properly where allowed.
- Do not rinse clean cookware in untreated water right before eating from it.
Do filters, tablets, and UV light kill giardia?
Some methods work better than others.
Backcountry water treatment is not one single magic trick. Filters remove many parasites. Chemical disinfectants can help with viruses and bacteria, but some chemicals do not work well against parasites. UV can work in clear water when used correctly, but murky water can block light.
| Method | Giardia protection | Trail catch |
|---|---|---|
| Boiling | Strong | Needs fuel, time, and cooling |
| Backpacking filter | Strong if rated for cysts/oocysts | May not remove viruses |
| Chemical tablets | Varies by chemical | Contact time and water temperature matter |
| UV purifier | Can work in clear water | Needs batteries and clear water |
For higher-risk water, a belt-and-suspenders approach makes sense: filter first, then disinfect. That gives you parasite removal plus broader coverage against smaller germs your filter may miss.
Related reading
- What Does Poison Ivy Look Like? Leaves of Three and Lookalikes
- What Does a Tick Bite Look Like? Photos and Warning Signs
- What Does a Poison Ivy Rash Look Like?
- Chigger Bites: What They Look Like and How to Stop the Itch
FAQ
Can giardia go away on its own?
Yes, it can, but symptoms may last weeks. If you have diarrhea or symptoms that fit giardia after untreated water, ask a healthcare professional whether testing or treatment is needed.
Can you tell giardia by smell?
No, smell alone cannot identify giardia. Foul-smelling, greasy diarrhea can fit giardia, but other gut infections and digestive problems can smell awful too.
How soon after drinking creek water will you get sick?
Giardia symptoms usually start 1 to 2 weeks after infection. If you feel sick within hours, another cause may fit better, though you should still treat dehydration and seek care when symptoms are severe.
Is giardia contagious between hikers?
Yes, giardia can spread from person to person through microscopic stool contamination. Handwashing, careful bathroom hygiene, and not sharing bottles or utensils while sick reduce the risk.
Does clear mountain water need filtering?
Yes, treat it before drinking. Clear, cold, fast water can still carry giardia and other germs from humans, livestock, pets, or wild animals.