Many dogs love swimming and playing in water. Especially during hot months, rivers, lakes, and pools can be great sources of exercise and entertainment for dogs. They also carry risk of illness or injury. The following are some of the potential hazards dogs may encounter while in or near water. 


This is a common parasitic infection found worldwide that can sicken pets that ingest contaminated water, soil, or feces. While many dogs infected with giardia have no symptoms, others become seriously ill. Young, old, and immunocompromised dogs are most susceptible to serious illness from giardiasis. Symptoms of infection include:

  • Watery or soft diarrhea
  • Green color in stool
  • Mucus in stool
  • Weight loss/anorexia
  • Vomiting
  • Dehydration
  • Poor coat appearance
  • Excessive gas

According the Companion Animal Parasite Council (CAPC), New Mexico is a high-risk state for giardiasis. At the time of this writing, 1 in 11 dogs tested are positive for infection.

Blue-green algae

Harmful blue-green algae (HBGA), which can also be red or brown, can be fatal to dogs within minutes of exposure. Illness occurs when dogs ingest contaminated water, including when licking their fur. Small amounts are enough to cause illness. HBGA can produce neurotoxins and/or hepatotoxins. The neurotoxins work rapidly, attacking the nervous system. Hepatotoxins attack the liver and can take hours or days to cause death. Exposure to HBGA is always a medical emergency and requires immediate treatment. 

Symptoms can include: 

  • Diarrhea 
  • Vomiting 
  • Weakness/collapse/paralysis 
  • Confusion 
  • Seizure
  • Difficulty breathing/excessive panting

Blooms occur in stagnant or slow-moving water including ponds, rivers and streams, lakes, and small pools of water. Water may look foamy, discolored, or have a slimy or scummy surface. Blooms can also occur under the surface, making them difficult to notice. 

HBGA have been found in every state in the US and around the globe. It is becoming more prevalent and cases of exposure more frequent. A recent report showed an annual increase in HBGA calls to the American Society for the Prevention of Cruelty to Animals (ASPCA) Animal Poison Control Center (APCC) over the past 13 years and a widening geographical spread of calls. The report credits climate change and owner awareness with the increase and notes that 65% of calls to the APCC occurred July through September coinciding with summer recreation. 


Leptospirosis is a serious, potentially fatal disease caused by leptospira bacteria. The disease can cause tissue and organ damage, including kidney and liver failure, as bacteria multiply in the bloodstream and spread throughout the body. Dogs can become infected when they come into contact with infectious urine (including in water or soil) via mucus membranes or broken skin or by ingesting infected animal tissue. Contact with contaminated water (usually stagnant or slow moving) is the most common way dogs become infected.   

Symptoms include:

  • Fever
  • Lethargy
  • Weight loss/anorexia
  • Depression
  • Jaundice (yellow discoloration of eyes, gums, skin)
  • Abdominal discomfort or pain
  • Vomiting and diarrhea
  • Difficulty breathing

Leptospirosis occurs worldwide, though historically warm, wet regions have been more susceptible. Outbreaks are occurring more frequently in areas previously thought of as low risk. The leptospirosis vaccine is considered a non-core, lifestyle vaccine, though a recently updated consensus statement on the disease by the American College of Veterinary Internal Medicine (ACVIM) recommends an increase in vaccinations.  

Swimmer’s ear

Otitis externa (infection of the external ear canal) is common among dogs and can have various causes. One cause is bacteria growth when water becomes trapped inside the ear canal. This commonly afflicts dogs that swim or play in water.  

Symptoms can include:

  • Pain and discomfort of the ear(s)
  • Head shaking
  • Excessive ear scratching
  • Foul odor from ears
  • Red/inflamed skin
  • Black or yellow discharge from ear

Early treatment is vital. Ear infections are painful, and when dogs scratch it can cause broken blood vessels in the ear flaps and swelling. Untreated, severe inflammation and infection can damage or rupture the ear drum and can lead to a deeper internal ear infection and hearing loss.


A parasitic flatworm called the heterobilharzia americana causes this illness, which can be fatal if left untreated. The worm is only known to live in two species of snails, which carry it to water. Dogs become infected by drinking contaminated water. The parasite affects dogs’ liver and intestines. 

Symptoms vary with progression and can include:

  • Skin rash
  • Cough
  • Appetite loss
  • Lethargy
  • Drooling
  • Dehydration/increased thirst

Once only found in Texas, Louisiana, and other gulf regions, heterobilharzia americana and the illness it causes have been recently found in other areas, including Utah and California. 

Drowning and secondary drowning

Exhaustion is the most common cause of drowning in canines. Some dogs have no off switch and will continue to play and swim until they are no longer capable of paddling. Others struggle to find a way out of a body of water and become exhausted and weak. Not all dogs are natural swimmers and can struggle to stay above water. 

Secondary drowning (also called non-fatal drowning) occurs when a dog, after being submerged, survives for at least 24 hours. Residual water that stays trapped in the lungs can cause pneumonia or secondary drowning. This can be fatal days after an incident. If a dog has been submerged under water, medical attention is necessary, even if the dog seems okay. 

Symptoms of secondary drowning include:

  • Lethargy
  • Coughing
  • Difficulty breathing
  • Distress
  • Anxiety

A combination of awareness, supervision, and preventative measures can reduce dogs’ risk of suffering severe illness or injury while near or in water. For dogs who spend time in water, owners should discuss appropriate vaccinations and the health status and fitness of dogs with a veterinarian. 

Call us at (505) 299-9533 to schedule an exam or ask about appropriate vaccinations.  



  1. Companion Animal Parasite Council. Parasite prevalence maps. Published March 29, 2019.
  2. Bloch RA, Faulkner G, Hilborn ED, Wismer T, Martin N, Rhea S. Geographic variability, seasonality, and increase in ASPCA Animal Poison Control Center Harmful Blue-Green Algae Calls—United States and Canada, 2010–2022. Toxins. 2023;15(8):505. doi:10.3390/toxins15080505
  3. Sykes JE, Francey T, Schuller S, Stoddard RA, Cowgill LD, Moore GE. Updated ACVIM consensus statement on leptospirosis in dogs. Journal of Veterinary Internal Medicine. 2023;37(6):1966-1982. doi:10.1111/jvim.16903
  4. Loker ES, Dolginow SZ, Pape S, et al. An outbreak of canine schistosomiasis in Utah: Acquisition of a new snail host (Galba humilis) by Heterobilharzia americana, a pathogenic parasite on the move. One Health. 2021;13:100280. doi:10.1016/j.onehlt.2021.100280
  5. Bernstein J. Dog-killing flatworm discovered in Southern California. News. Published March 14, 2024.
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