When your dog suddenly develops smelly, watery diarrhea, it’s hard not to worry. The odor and loose consistency often point to something going wrong in their digestive system — even if they seem otherwise normal.
We outline the common causes of smelly watery diarrhea in dogs, what you can do at home, and when to seek veterinary help.
Smelly Watery Diarrhea in Dogs — Why It Happens
Smelly watery diarrhea in dogs happens when the intestines become irritated or inflamed, leading to poor digestion and bacterial imbalance. This can occur after eating spoiled food, due to bacterial or viral infections, parasites, food sensitivities, or even underlying liver or pancreatic problems.
The foul odor often indicates that digestion is incomplete or that harmful bacteria are present in the gut.
While some mild cases clear up within a day, persistent or especially foul-smelling diarrhea may require prompt veterinary attention to prevent dehydration or uncover deeper issues.
Smelly Watery Diarrhea in Dogs: Common Causes
Dietary Indiscretion (Eating Something Spoiled or Unusual)
One of the most common reasons for smelly watery diarrhea is what veterinarians call dietary indiscretion — when a dog eats something they shouldn’t. This could be spoiled leftovers, garbage, or even feces.
When a dog ingests contaminated food or trash, it can disrupt the gut bacteria and cause inflammation in the intestines. The result is watery, foul-smelling stool that may appear brown, yellow, or even contain mucus.
If your dog seems otherwise bright and alert, a single episode may resolve on its own. However, if the odor is strong and the stool remains runny for more than a day, it’s best to consult your vet.
Read more: Dog Watery Diarrhea No Other Symptoms (Causes and when to worry)
Bacterial or Viral Infections
Certain infections in the gastrointestinal tract can cause particularly smelly diarrhea. Common bacterial culprits include Salmonella, E. coli, and Clostridium perfringens, while viruses such as parvovirus and coronavirus are also known offenders.
These pathogens damage the intestinal lining, reducing the body’s ability to absorb nutrients and fluids. The result is watery stool with a sour or rotten odor. Puppies and senior dogs are especially at risk due to weaker immune systems.
If your dog has additional symptoms such as vomiting, lethargy, or blood in the stool, this could point to an infection that requires prompt veterinary care.
Intestinal Parasites (Giardia or Worms)
Parasites are another frequent cause of foul, watery diarrhea — especially in dogs that spend time outdoors or drink from puddles. Giardia and Coccidia are microscopic parasites that thrive in contaminated water sources, while worms like hookworms or roundworms can be picked up from soil or other animals.
These parasites damage the lining of the intestines and interfere with nutrient absorption, leading to a greasy or fishy smell in the stool. In some cases, owners may notice mucus or bubbles in the diarrhea, a telltale sign of parasite irritation.
A fecal test at your veterinarian’s office can confirm the diagnosis and ensure your dog receives the right deworming or antiparasitic treatment.
Food Intolerance or Allergy
If your dog regularly has loose, smelly stools but seems otherwise fine, food intolerance could be to blame. Common culprits include certain proteins (like beef or chicken), grains, or dairy ingredients.
In these cases, the digestive system struggles to break down specific ingredients, resulting in partially digested food fermenting in the intestines — which produces strong odors.
Switching to a limited-ingredient or hydrolyzed protein diet under veterinary guidance can help identify the trigger and give your dog’s gut time to recover.
Gut Dysbiosis or Imbalance
The canine digestive system relies on a balanced mix of “good” bacteria to keep digestion smooth and odor-free. When this balance is disrupted — often after antibiotics, stress, or a poor-quality diet — it can lead to watery, foul-smelling diarrhea.
This condition, known as gut dysbiosis, means that harmful bacteria outnumber the beneficial ones, resulting in fermentation, gas, and poor nutrient absorption.
Probiotics, high-fiber diets, and hydration can help restore gut health, but if symptoms persist beyond a few days, your vet may recommend stool testing to rule out other issues.
Liver or Pancreas Problems
When the liver or pancreas isn’t functioning properly, food isn’t digested as it should be. The pancreas produces digestive enzymes, while the liver helps process fats. When either organ is compromised — as in pancreatitis or liver disease — stool often becomes watery, greasy, and extremely foul-smelling.
Dogs with pancreatic or liver issues may also show signs like vomiting, appetite loss, or yellow-tinged eyes and gums. Because these conditions can quickly worsen, a veterinary visit and bloodwork are essential if these signs accompany diarrhea.
What to Do If Your Dog Has Smelly Watery Diarrhea
If your dog’s diarrhea is mild and they’re otherwise acting normal, you can start by withholding food (not water) for 12–24 hours to allow the digestive tract to rest. After that, offer small portions of bland food like boiled chicken and rice.
Hydration is critical. Offer fresh water frequently or add low-sodium chicken broth to encourage drinking. If dehydration is a concern — such as if your dog’s gums are sticky or eyes look sunken — seek veterinary help right away.
You can also introduce a canine probiotic supplement to support gut balance during recovery. Avoid giving over-the-counter medications meant for humans, as these can be toxic or worsen symptoms.
If your dog is on a new food, consider switching back to their previous diet until the stomach settles. Gradual food transitions (over 7–10 days) can prevent recurrence of watery stools.
Always monitor for other signs such as vomiting, lethargy, or blood in the stool. Even if diarrhea is the only symptom, persistent odor and watery texture suggest an imbalance that may need testing.
When to Call or Visit Your Vet
You should contact your veterinarian if your dog’s watery diarrhea lasts longer than 24–48 hours, especially if it’s accompanied by a strong odor.
Immediate veterinary attention is warranted if:
There is blood, dark tarry stool, or mucus present.
Your dog is lethargic, vomiting, or refusing to eat or drink.
The diarrhea has a rancid smell suggesting infection.
Your dog is a puppy, senior, or has a chronic condition.
Your vet may recommend a fecal exam, bloodwork, or imaging to check for infection, organ issues, or dietary causes. Timely diagnosis helps prevent dehydration and allows treatment to start before more serious complications arise.
Read more: Dog Keeps Licking Anus and It Smells (What it means and how to help)
Key Takeaway
Smelly watery diarrhea in dogs is a sign that their digestive system is struggling — whether from something they ate, an infection, or an underlying issue like food intolerance or organ dysfunction.
While mild cases can resolve with rest and hydration, persistent or foul-smelling diarrhea deserves a vet check to rule out more serious conditions.
By acting early, offering supportive care, and keeping your dog hydrated, you can help them recover quickly and prevent future digestive upset.