A seemingly carefree and enjoyable day on the water can pose serious health risks to dogs. Some water-borne illnesses are treatable and present minimal dangers to dogs, while others are more devastating. Before letting dogs dive into the lake or splash along the shore, it is important to be aware of potential health risks and ways to keep our companions safe this summer.

Blue-Green Algal Blooms (Cyanobacteria) 

Blue-green algae, a poisonous cyanobacteria, thrives in standing water, such as ponds, puddles, fountains, birth baths, and flower pots. Poisoning occurs when dogs drink or swim in water contaminated with algal blooms. If ingested, these blooms can lead to shock, liver failure, respiratory arrest, and death. Veterinary treatment involves prompt, supportive care to improve survival rates (Cornell). To decrease risk of cyanobacteria exposure, do not allow dogs to lap from water containing algal blooms, scum, or foam.  Check local water advisories for health warnings before visiting a particular body of water. Remove all stagnant water sources around the home (Cornell).

If your dog has been exposed to possible cyanobacteria, immediately put on gloves and thoroughly rinse the coat and towel dry. Wash your hands and then give your dog a full bath. Seek prompt veterinary care with suspected cyanobacteria ingestion (Vesci, 2023).

Leptospirosis

Leptospirosis is a disease caused by bacterium Leptospira found in contaminated soil or water. Eastern, midwestern, and southwestern regions of the United States are considered hotbeds for Leptospirosis transmission. Leptospirosis is contracted when mucus membranes or skin wounds come in contact with water contaminated by urine from infected rodents, wildlife or farm animals. Symptoms of Leptospirosis include loss of appetite, vomiting, diarrhea, fatigue, abdominal pain, dehydration, weight loss, stiffness. Leptospirosis can be fatal in severe cases. If Leptospirosis is suspected, the veterinarian will begin a course of antibiotics soon as possible.

Depending on how sick an affected dog is, hospitalization may be required for fluid therapy, medications, and nutritional support. (AVMA)

Giardiasis

Giardiasis is a common parasitic infection caused by the single cell protozoan, Giardia intestinalis. Dogs become infected via “fecal-oral” transmission after swallowing parasitic cysts from contaminated food, water, soil, or feces.

Once inside the intestines, the cysts dissolve and release parasites which feed on the intestinal wall and multiply. Some of the intestinal parasites form protective coverings again and excrete cysts in stool, ready to infect other dogs. These cysts can survive for several months in soil and water.

Symptoms of Giardia include gastrointestinal cramping, diarrhea, loss of appetite, and vomiting. If Giardia is suspected, take a sample of your dog’s stool to the vet office for microscopic examination. Prevention measures include strict hand washing, proper bagging and disposing of feces, watching for signs of illness, and not allowing your dog to eat animal feces or drink standing water (AKCCHF.org).

Salt Water Intoxication

When a dog ingests too much of salt water, the excess salt pulls fluid from the bloodstream into the intestines causing vomiting, diarrhea, and dehydration. Consuming large amounts of salt water can cause neurological symptoms, such as lethargy, muscle tremors, disorientation, and seizures. A characteristic sign of salt water toxicity is unusual behavior - too much sodium in the body leads to lethargy and confusion. Call your vet immediately with any changes in behavior.

Encourage your dog to drink plenty of fresh water before heading to the beach. This will hydrate and make your dog less likely to seek saltwater due to thirst. If you notice your dog drinking salt water, take a break from ocean play and offer fresh water. Teach the “leave it” command to steer dogs away from drinking ocean water. (AKC, 2024)

Chlorinated Pools

Properly chlorinated pool water is not harmful to dogs when swallowed in small amounts. Under-treated pool water can contain harmful algae, parasites, and bacteria. Pool chemicals in concentrated form (chlorine tabs and crystals ) are highly caustic and cause painful burns to the mouth, esophagus and stomach if ingested. Seek emergency care if ingestion of concentrated pool chemicals is suspected. As a preventative measure, teach the “leave it” command to redirect your dog from drinking pool water. If your dog continues to lap pool water, take them indoors for a break. Always have plenty of fresh tap water available poolside. (AKC 2024)

Pythiosis (“Swamp Cancer”)

Pythiosis is a rare but emerging disease caused by Pythium Insidiosum, an aquatic mold found in contaminated swamps and ponds during fall and winter months. High risk areas for Pythium Insidiosum are typically states bordering the Gulf of Mexico in the southeastern United States. However, over the past 20 years, cases of pythiosis in dogs have been reported in Wisconsin, California, New Jersey, Virginia, Tennessee, Kentucky, and the Carolinas.

Pythium Insidiosum infects the skin or gastrointestinal tract in dogs, causing necrotic lesions, fever, coughing, sinus swelling, severe weight loss, vomiting, and diarrhea (Erikson, 2024).  

Keep dogs away from high risk water sources. Thoroughly wash dogs after swimming in stagnate water. If pythiosis is suspected in your dog, seek immediate veterinarian care. Early diagnosis and treatment is critical in improving survival rate. Treatment is challenging and may involve a combination of antifungal medication, surgery, and nutritional support.  (VCA , 2025) 

Red Tide

Red tide, known as K. brevis, is a microscopic algal species found in the Gulf of Mexico. The harmful K.brevis blooms discolor the ocean surface with a reddish-brown hue, inspiring the name “red tide.” If ingested, the K. brevis can cause neurological and gastrointestinal damage resulting in seizures, vomiting and diarrhea. Breathing red tide toxins can elicit coughing and wheezing. 

Do not allow dogs to play in red tide waters or come in contact with foam accumulating on the beach.  If your dog gets in water with red tide, it is important to wash them immediately due to the likelihood of them cleaning themselves and ingesting the toxin. Suspected exposures to K. brevis should be immediately reported to the veterinarian.  (Floridahealth.gov, 2023)

Wild Seaweed

Wild seaweed found strewn along the shoreline contains high levels of salt and can be toxic if ingested. Long seaweed strands absorb water and can swell in the stomach and cause obstruction. To prevent dogs from eating seaweed, keep them on a lead during walks. Consult a veterinarian if your dog eats wild seaweed on the beach. (Sassafras, 2025)

Being Proactive  (Morris Animal Foundation, 2017)

• Avoid suspicious water conditions Pay attention to warning signs – if the water is not safe for humans to swim, it is not safe for dogs! 
• Check for water quality advisory updates 
• Remove stagnate water sources around the home 
• Do not let dogs swim or wade in potentially contaminated water
• Keep your dog on a lead while walking near shorelines 
• Do not let your dog lick their hair or paws upon exiting water - rinse off after all water play
• Monitor for symptoms and contact your veterinarian immediately with any concerns.