3+ Reasons Your Dog Shouldn’t Drink Straight from the Lake (or River)

Summer is here and with it comes a the perfect weather for outdoor activities. Here at the Pawsitively Intrepid household, summer means lots of hiking and backpacking. Heat and hiking plus dogs means carrying lots of water. If you hike frequently with your dog, whether you are trying to cut down on the weight of your pack or just have a dog that likes to spend lots of time in the lakes and rivers along your hike, you have probably wondered: can my dog drink straight from the lake or stream nearby?

Can dogs drink unfiltered lake or river water? Dogs can, and often do, drink water out of lakes, rivers, streams, puddles, and ponds. If you have a dog who likes swimming, it can be almost impossible to prevent them from drinking the water. But drinking untreated water poses health hazards for dogs, just like it does for people. As a result, it is NOT recommended that dogs drink untreated/unfiltered water straight from a lake or river.

Keep reading to find out what diseases your dog can pick up from contaminated water and why and how you should filter/treat your dog’s water when using a natural water source. 

Waterborne Diseases are the Reasons that Dogs Shouldn’t Drink Straight from the Lakes or Rivers

Reason #1: Giardia

Giardia is a one-celled parasitic species known as protozoa. The parasite occurs worldwide. Hikers may know this disease as “beaver fever,” as it is contracted by consuming contaminated water. 

Dog’s pick up Giardia when they swallow the cyst stage of the parasite. The cysts can be ingested by eating or sniffing the cysts from contaminated ground or by drinking contaminated water.  

The best way to prevent infection is by using good hygiene. Avoid allowing your dog to drink untreated water; water can be made safe by heating it to a rolling boil for at least 1 minute or by using a filter that has an absolute pore size of 1 micron (pt) or smaller, or has been NSF rated for “cyst removal.”

It takes about 5 to 12 days from ingestion of cysts to passage in feces in dogs. Once the cysts pass in feces, they are immediately able to infect other animals. 

Giardia attach themselves to the intestinal wall and cause a quick onset of bad-smelling diarrhea. Dogs may develop weight loss, chronic intermittent diarrhea and occasionally vomiting. Typically Giardia is not life-threatening unless a dog is immunocompromised However, it is still important to recognize and treat the disease. 

Once diagnosed, giardiasis is treated with medications like fenbendazole or metronidazole. Supportive treatment may also be administered if dehydration or severe diarrhea is present. 

Find out more about Giardia in dogs at https://vcahospitals.com/know-your-pet/giardia-in-dogs.

Due to the water-borne nature of Giardia, infection rates have been known to go up in late summer. In some years, cases of giardiasis in people were twice as high between June- October as they were between January-March. And untreated water from lakes and rivers are a significant risk. Find out more about Giardia at CDC.gov.

Reason #2: Leptospirosis

Leptospirosis is a disease caused by infection with the Leptospira bacteria. Like Giardia, Leptospira bacteria can be found worldwide in soil and water. In the United States, the majority of human cases of leptospirosis occur from recreational activities involving water. 

Common risk factors for dogs include exposure to drinking from rivers, lakes or streams, exposure to infected wildlife and water sources, and contact with rodents or other dogs.

Dogs can become infected when their mucous membranes (like nose passages or the gums of the mouth) or an open wound/scratch come into contact with infected urine or water/soil that has been contaminated by infected urine. Bites from infected animals or ingestion of infected carcasses can also spread leptospirosis.

Symptoms of leptospirosis include fever, muscle tenderness, vomiting, diarrhea, and lethargy. The disease can cause kidney failure with or without liver failure. It can also cause bleeding disorders. 

Leptopsirosis is treatable with antibiotics and supportive care. When treated early or aggressively, chances for recovery are good. If left too long, leptospirosis can be fatal.

Luckily for those dogs with a high risk of exposure to Leptospira bacteria, there is a vaccine available. This vaccine has been proven effective at preventing leptospirosis and protects dogs for at least 12 months after appropriately boostered.

More information about Leptospirosis in dogs can be found at AVMA.org.

Reason #3: Blue-Green Algae

Cyanobacteria are commonly known as blue-green algae. They are microscopic bacteria found in freshwater lakes, streams, ponds, and brackish water ecosystems. By themselves, they are not specifically toxic, but they can produce toxins (like microcystins and anatoxins) that affect the people and animals that swim in and drink from water contaminated by these algae

The blue-green algae bloom to form a “pea soup” appearance to the water. They can also look like blue or green paint on the surface of the water. These blooms are most abundant during periods of hot weather (mid to late summer). 

It is impossible to definitely determine which blooms are producing toxins without testing. So it is recommended that all blooms are considered potentially toxic. Even a few mouthfuls of algae-contaminated water may result in fatal poisoning. 

Although not as reliable as laboratory testing, if you want to try a few simple tests for blue-green algae, check out MN Pollution Control Agency’s “Simple, no-cost tests for blue-green algae”.

As stated above, dogs that swim in lakes and ponds (or that are allowed to drink from these lakes/ponds) can easily be exposed to the algae. Symptoms of poisoning depend on the amount of toxin ingested. 

Ingestion of microcystins can result in liver damage or failure. Vomiting, diarrhea, blood in stool, weakness, seizures, and disorientation can all be observed. Left untreated, dogs can die from ingestion of blue-green algae. 

The other type of toxins produce by blue-green algae, anatoxins, result in neurotoxicity. So you may see increased drooling, muscle tremors, paralysis, and difficulty breathing. Dogs can die as a result of respiratory paralysis. 

There is no antidote for the toxins produced by blue-green algae. Aggressive, immediate treatment is necessary to help treat either of these fast-acting toxins.

There have been a lot of recent news stories about dogs dying from blue-green algae. MyBrownNewfies.com recently published an article about Blue-Green Algae which included a helpful graphic from EWG.org showing reported Blue-Green Algae blooms from 2010 to present.

Reasons #4-6: Cryptosporidium, Escherichia Coli, and Pythiosis

Cryptosporidiosis like Giardia is caused by a protozoa. This one is called Cyrptosporidium. It is shed in the stool of wild and domestic animals and can also contaminate water sources, like lakes and rivers. Dogs generally develop diarrhea when infected with Cryptosproidum. This is a treatable illness.

Escherichia Coli is a bacterium that causes diarrhea and stomach pain. The bacterium is spread through fecal-oral transmission. And just like the other organisms listed above, an infection can occur if a dog drinks or swims in contaminated water. E.coli can also cause urinary tract infections, ear infections and other problems in dogs. 

Pythiosis is caused by a water mold called Pythium insidiosum. If you live along the Gulf of Mexico this is an extra risk to add to your list. Dogs suffering from pythiosis commonly loss weight and have vomiting/diarrhea. Some can also develop skin disease with draining wounds that don’t heal. High-risk areas include swamps, bayous, or ponds. The prognosis for dogs infected with Pythium is poor with fewer than 10% of dogs cured with medications alone. More information about Pythiosis can be found at VCAHospitals.com.

Water Sources to Avoid Completely

To truly protect your dog, they should not be drinking from any unfiltered/untreated water sources while out on a hike. However, this can be slightly impractical. Especially for the dog that loves to swim. To limit risk, here are some guidelines about where your dog can swim.

Always avoid lakes with blue or green algae. While some algae are non-toxic, avoiding any significant algae significantly limits your dog’s risk of exposure to cyanobacterium toxins. 

Another tip is to avoid stagnant standing water. While Giardia is known for being present even in fast-moving rivers and streams, Leptospirosis and Blue-Green Algae are more prevalent in slow-moving or standing water areas. Keeping your dog out of standing and slow-moving water is an easy step in preventing infection from contaminated water sources. 

Making Sure Your Dog Has Plenty of Safe Water to Drink on a Hike

Dogs are more susceptible to overheating then people, as they can’t sweat, so it is very important to have plenty of safe water available for them to drink throughout a hike.

Carry water from home along on a hike

If you are going for a day hike or a short overnight backpacking trip, we recommend bringing your dog’s drinking water along with you. Yes, this adds some weight to your pack, but it potentially prevents significant diarrhea and ill-health later down the road.

Interested in finding some great water bottles/bowls for hiking dogs, check out our post “5 Useful Styles of Dog Hiking Water Bowls

Filter or treat water if you can’t carry it all in

While carrying water along for your dog is the safest way to make sure that you provide uncontaminated water, that is not always possible. When you plan a multi-night backpacking trip, carrying all your water can add a lot of weight to your pack. 

If you can’t bring water from home, follow these tips to make sure the water you offer your dog is safe to drink. 

  • For Giardia, water can be made safe by heating it to a rolling boil for at least 1 minute. Or you can use a filter that has an absolute pore size of 1 micron or smaller or has been NSF rated for “cyst removal”. Disinfection with iodine has a low to moderate effectiveness at killing giardia, so filters or boiling is preferred.
  • Leptospira can also be killed by heating water to a rolling boil for a few minutes. Another alternative is water purification tablets that use iodine. Make sure your dog will drink water with iodine added before you start out on a hike. Iodine can leave an unpleasant taste. Portable UV sterilizers can easily be used while backpacking and will successfully kill Leptopsira bacteria. Note that typically filtration systems used by hikers do not work for Leptopsira. Leptospria can be incredibly small and will pass through filters with a pore size of more than 0.2 microns (including membrane and charcoal types). 
  • For blue-green algae, it is best to just avoid this water. Blue-green algae toxins are not removed by boiling or disinfecting with chlorine, ultraviolet light or other treatment. 

Overall Recommendations

Whether you filter, boil or add iodine to your dog’s water, you will limit the risk of your dog become ill by preventing him or her from drinking straight from the water source. And if your dog does love to swim and some water ingestion can’t be prevented, follow these guidelines:

  • Avoid standing water
  • Avoid water with visible algae blooms
  • Vaccinate your dog against leptospirosis
  • Seek prompt treatment if your dog does develop diarrhea after drinking or swimming in untreated water

Related Questions

How much water should a dog drink on a hike? Dogs can drink between 0.5 to 1.5 oz of water per pound per day. So for Glia, who is 40 pounds, this could be between 20 to 60 oz of water. When hiking, error on the high side of the range to ensure that your dog stays hydrated. Especially if it is a warm day outside.

If we are just day-hiking for a couple of hours, I often pack 15-20oz of water for Glia. But if we will be backpacking for 24 hours without other available water sources, we bring the full 60oz + a little extra just in case. Since this adds a lot of weight, we try to plan our hikes to include a water source near our campsite.

What other parasites do you need to protect your dog from on the trail? Dogs can pick up a lot of diseases in the great outdoors. We recommend having your dog on a regular deworming (like is found in most heartworm preventatives) and making sure your dog is on a flea/tick preventative before heading out on a hike. Find out more about tick prevention for dogs in our post “Surviving Tick Season with Dogs.”

How far can a dog hike? The average dog can happily hike 2-3 miles without any specific conditioning. A dog that has been well-conditioned and trained can hike for 20+ miles. But if your dog has health concerns or is overweight, consult with your veterinarian about how far your individual dog can hike.


Kate is the writer of Pawsitively Intrepid. She has spent the last 9 years working full-time as a veterinarian, treating dogs and cats. But as of June 2023, she is taking a year to travel with her dog, volunteer, and work on some passion projects.

4 thoughts on “3+ Reasons Your Dog Shouldn’t Drink Straight from the Lake (or River)

  1. Need to know if I can treat my dog who has contracted leptospirosis with iodine and if so how much and how do I administer it she’s been to the vet and he’s not getting better she’s on antibiotics I’m going to the vet again but I haven’t helped her and someone told me iodine would help?

    1. I hope your pup makes a full recovery! I haven’t heard about any research regarding treating leptospirosis with iodine, but (as you are already doing) I would run any potential treatments past your veterinarian.

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