Toxic Algae and the Health of Companion Dogs

Recently, we discussed the health risks of cyanobacteria blooms, which occur in mostly slow-moving waterways and have deleterious effects on the life of companion dogs. The Environmental Protection Agency (EPA) calls them “CyanoHABs”, which is short for cyano-harmful algal blooms. At Hemopet, we think the name is a misnomer since cyanobacteria blooms are bacteria – not algae. Other types of harmful algal blooms exist in the environment and they are algae.

What about actual toxic algae in water and what else might be in the water? There’s a lot to digest in this subject.

First and foremost, whether or not some of the multiple strains of toxic algae are, in fact, algae or protozoa, is still controversial. So, we decided to let the experts work that one out. For the purposes of this article, we will refer to them as algae.

To familiarize you with the topic, you have probably heard that Florida’s Gulf Coast is plagued by red tides. Florida’s red tides are caused by Karenia brevis. However, this region can also experience blooms of strains of Pseudo-Nitzschia predominantly in the gulf or Pyrodinium in its estuaries. California can also have blooms of Pseudo-Nitzschia as well as Alexandrium catenella. Indeed, these blooms occur all over the waters of the United States. Many of these algae usually produce red or even brown discolorations in the water.

Further inland, golden algae is aptly described as “golden” due to the yellow tint that can be seen on top of the water. It is caused by Prymnesium parvum and is suspected to be responsible for many fish kills. There is no evidence that golden algae impacts the health of humans and animals besides fish. Experts have not warned against eating dead fish or handling them during these periods of blooms.

What is causing these algae to grow uncontrollably? Well, they need inorganic nutrients like nitrates, phosphates and sulfur to grow. Runoff of these chemicals from farming, factories, sewage treatment plants and other sources can cause an overgrowth of harmful algal blooms (HABs).

Let’s discuss the diseases caused by these substances in the water.

Human Poisonings Caused by Harmful Algae Bloom

Here is a general list of poisonings and where they are found. Please check with your state or local Department of Natural Resources to find out about active blooms in your area.

Regions Poisoning Algae
Maine to New York; Alaska to California; Florida Paralytic Shellfish Poisoning Alexandrium Catenella; Alexandrium spp.; Gymnodinium catenatum; Pyrodinium bahamense
Florida Neurotoxic Shellfish Poisoning Karenia brevis
Texas; East Coast Diarrhetic Shellfish Poisoning Dinophysis
Florida; West Coast Amnesic Shellfish Poisoning Pseudo-nitzschia
Texas and South Florida Ciguatera Fish Poisoning Gambierdiscus

These toxicities occur when people eat shellfish or certain types of fish because the toxins from the algae buildup in the fish. The resultant poisonings can lead to a range of symptoms. In some instances, like paralytic shellfish poisoning, ciguatera fish poisoning and amnesic shellfish poisoning, even death can happen.

What about the health of our companion dogs and what should we do?

Companion Dogs and Potential Algae Poisonings

Our research discovered a paper documenting actual paralytic shellfish poisonings in three dogs in England from 2018. Summarizing the results would be an injustice to the detailed description by the researchers. So, we are sharing their unedited findings.


On 31 December 2017, a family with five dogs walked along Cley Beach, at the village of Clay Next Sea, Norfolk, E. England. The family observed the strandline, containing hundreds of dabs, starfish, as well as several dead seal pups. Two of the five dogs were seen to consume material from the strandline. Dog 1, a 28 kg, four-year old Golden Retriever was observed to eat dab as well as a “peach-coloured species”, most likely a starfish or a crab, as testified by the owner. Dog 2, a 12 kg Cocker Spaniel, was seen to eat multiple Dab fish, with no observations of eating starfish made by the owners.

Dog 1 began vomiting on return to the family car, approximately 30 min after the first ingestion. Five to six episodes of yellow-peachy coloured vomit were produced. The dog was not interested in drinking, appeared subdued, but jumped into a car as normal. The dog was subsequently unattended for 10 min followed by a further 40–50 min. At this point, the dog was found in what appeared to be a normal sleeping position, on her right side. On examination, the dog did not respond, and the owners realised she had died. The other dogs in the car were calm. In total, the overall time between ingestion and death was estimated to be 1.5 to 2 h.

Dog 2 did not appear to exhibit any signs of being unwell until later in the evening of 31 December 2017. She experienced two to three episodes of vomiting but still appeared to be alert and happy. The dog ate and drank water as normal. The following morning, dog 2 had brought up her dinner from the previous night. It was light brown in colour and of a stringy mucus consistency. The other dogs were not interested in eating the regurgitated dinner, which would have been normal behavior according to the owners. During the morning, the dog was observed to struggle to urinate, possibly a little distressed by her back end. She also appeared roached. On further examination, it was noted that her gums were tacky, and the elasticity of her skin was reduced, inferring dehydration. At this point, the dog was becoming subdued and was taken to the veterinary practice. The remaining three dogs were not seen to consume any substances from the beach and exhibited no signs of illness.

On 13 January 2018, a walker and his seven-year old, 31 kg Siberian Husky dog (Dog 3), walked along the beach at the hamlet of Felixstowe Ferry, Suffolk, E. England, close to the outlet of the Deben estuary. The stony beach was generally devoid of any marine life, although at 10:45 a.m., the dog was observed to eat a shore crab, close to the water’s edge. Because of the position of the crab on the beach and the state of the tide, it was estimated that the crab would have been exposed on the beach for only 15–20 min. Within 30 min of eating the whole crab, the dog was seen to vomit 7–8 times. After lying down for several minutes, the dog attempted unsuccessfully to stand and walk, whereupon he was observed to have paralysis in the hind legs, being able only to drag forward using the front legs. Within the next 10 min, during a car journey to the veterinary practice, the dog lost consciousness. On arrival at the vet, heart massage was performed and oxygen provided, with adrenaline injection to the heart. After 15 min, the dog was pronounced dead. In total, 60–90 min passed between consumption of the crab and the time of death. No further tests were made and no post-mortem examination was performed.

Dog 2 presented on 1 January 2018 and was depressed in mentation, showing signs of dehydration and hypovolaemia (loss of fluid from the circulatory system). Blood tests showed that the liver enzymes were normal. She was treated with antibiotics and intravenous fluids and was considered to be more stable after 24 h. After 24 h, blood tests showed elevated liver enzymes. She also had markedly raised inflammatory protein levels. She was started on liver support supplement and stayed in the hospital until 5 January 2018 when blood tests showed that the liver enzyme levels were reducing and she was discharged. The animal did not show any signs of neurological toxicity during hospitalisation.

Best Practices

During a HAB event, it is best to avoid the beach or water altogether. We understand if your companion dog loves it and running around gives him the best exercise. So, if you still decide to go, please be vigilant and make sure your dog does not eat any dead fish or lick them. Additionally, thoroughly wash him off afterward with clean water since ingestion can still occur with fur licking.


“Dinoflagellate.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 12 Jan. 2017,

“Dinoflagellates and Red Tides.” Scripps Institution of Oceanography Latz Laboratory, University of California San Diego,

“Harmful Algal Blooms (Red Tide).” National Ocean Service, National Oceanic and Atmospheric Administration, 10 Apr. 2019,

Henanger, Anika. How Does Red Tide Affect Pets? WINK News, 9 Aug. 2018,

Turner, Andrew, et al. “Fatal Canine Intoxications Linked to the Presence of Saxitoxins in Stranded Marine Organisms Following Winter Storm Activity.” Toxins, vol. 10, no. 3, 26 Feb. 2018, doi:10.3390/toxins10030094,

“What Are Phytoplankton?” National Ocean Service, National Oceanic and Atmospheric Administration, 27 July 2009,

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