Dangerous Waters

Picture this, you just finished work and are on vacation for the next few days. You have plans to head up to the mountains with some friends to go camping in the outdoors.  As you finish packing up the car, you get a call from your pet sitter who is suddenly unable to come watch and care for Rex, your 3-year-old black lab. You realize that you have no other option but to take Rex along. Like you, Rex enjoys the outdoors and is always ready for an epic adventure. You decide to take him and hit the road with your co-pilot by your side. After a few hours of driving, you make it to your destination and meet up with your five friends. Two of them also brought their dogs with them. You realize Rex will have a great time now that he has a few buddies to hang out with.

On your first day, you all setup camp and decide to go for a quick morning hike. Your one friend who also brought two of his dogs, wants to join you and Rex on the hike. While walking down one of the trails, you spot a wood dock next to a small river outlet and decide to go an explore. Both of you including the three dogs head in that direction. The dogs are on leashes to prevent them from getting too excited and running off. As you all are walking over, about five feet before reaching the wooden dock you come to a sudden halt and are startled by what lies in front of you. There are several dead birds dispersed on the dock with some very dead rotting fish nearby. What was even more surprising was the copious blue-green algae coating the surface of the water. You pull out your phone to call and alert the others and quickly remember reading about a similar situation in the paper a few weeks ago, about two people hiking near a river with their young dog.

The hikers noted the appearance of blue-green algae covering the surface of the water, closely resembling what is in front of you. Unfortunately, while the owners were looking around at the other scenery, the dog ran over and began to take a drink from the river. A few hours later, the owners rushed the dog to the vet after she had collapsed on the kitchen floor. The dog became severely ill and sadly passed away in the hospital shortly after the owners had arrived. Given the history, the owners provided including their recent hiking trip, the veterinarian became suspicious and asked them some further questions. When they mentioned the appearance of the river and its discolored water exhibiting a blue-green film on the surface, the vet became extremely concerned. Shortly thereafter the vet realized the dog most likely was poisoned after having ingested what appeared to be a thick coating of blue-green algae, covering the surface of the water. Your curious friend is intrigued by what is ahead and begins to walk over to the dock with his two dogs. Before he even takes a few steps forward, you grab him by the shirt and tell him to stay put. You mention the story you heard in the paper and proceed with caution. All of you head back to the camp grounds safe and sound.

What are Cyanobacteria?

Cyanobacteria is a phototrophic bacterium commonly encountered on the surface of fresh, brackish and salt-water systems1,2. Largely referred to as blue-green-algae, this organism has been found worldwide.  It produces a substantial number of toxic bioactive compounds that are responsible for poisoning both wildlife and domestic animals 1. Overgrowth of cyanobacteria produces what is known as, “freshwater harmful algal blooms” or (FHABs), that reside on the surface of bodies of water and resemble a blue-green “scum”1.  Although Cyanobacteria commonly appears blue-green in color, it can also exhibit shades of brown, red and white1. There are several cyanobacterial toxins that are responsible for causing severe multi-systemic illness in humans and animals1.

  • Microcystins
  • Nodularins
  • Anatoxin-a
  • Guanitoxin/Anatoxin-a(s)
  • Cylindrospermsins
  • Saxitoxins
  • Aetokthonotoxin

The most common toxin of the group, microcystins, more specifically microcystin-LR, can be linked to many poisonings with FHABs1. Once ingested, the toxin travels to the liver and accumulates within hepatocytes, causing an acute injury that ensues in irreversible damage. There are several factors that contribute to the type as well as onset of clinical signs, including species exposed, type of cyanotoxins, and the level of exposure1.  Many of the reported cases in domestic animals has been through exposure of cyanotoxins occur via ingestion1. Other routes of exposure that have been documented include, dermal and pulmonary, however both were observed in humans1.

Cyanobacterial toxins of veterinary importance1

Toxin: Microcystin Nodularin Anatoxin-a Guanitoxin/Anatoxin-a(s)

Clinical signs



Pale MM




Intrahepatic hemorrhage


*Same as Microcystin


Muscle fasciculations


Generalized muscle rigidity


Respiratory failure







Nicotinic signs: respiratory paralysis

Diagnostic findings Serum chemistry:









Coagulation testing:


*Same as Microcystin Normal Normal
Post-Mortem Lesions Icterus


Diffuse Hepatic necrosis

Renal tubular necrosis

*Same as Microcystin None None


Diagnosing cyanobacteria toxicosis relies primarily on the patients’ clinical signs and history of likely exposure1. Sources for exposure may include ponds, lakes, streams, reservoirs, open water tanks and buckets1. Other types of assays that can aid in making a diagnosis includes a complete blood count, serum chemistry, coagulation testing, biopsy/histopathology of liver, cyanobacteria toxin assays, and necropsy2.

The most important step in treating a patient with suspect/known cyanobacteria toxicosis, is to immediately remove them from the source1.  Consider bathing and or deep cleaning the hair coat to remove any residual material that may be present. If there is known ingestion of the toxin, proceed with GI decontamination1. Other treatment options targeting specific cyanotoxins such as microcystins, anatoxin-a and guanitoxin include1,2:

Microcystins Anatoxin-a Guanitoxin/Anatoxin-a(s)

1.      Supportive care and IV fluid therapy

2.      Cholestyramine

3.      Hepatoprotectants +/- N-acetylcysteine, S-adenosylmethionine, Silymarin and or Vitamin E 400

1.      Symptomatic + Supportive care and IV fluid therapy

2.      Anti-convulsant: diazepam, midazolam, levetiracetam or phenobarbital

3.      Muscle relaxants, benzodiazepines and barbiturates

1.      Symptomatic + Supportive care and IV fluid therapy

2.      Decontamination






By and large, the prognosis is poor for animals that are exposed to cyanobacteria and often succumb to multisystemic disease prior to receiving appropriate veterinary care2. This is why prevention is critical to evading future occurrences.

Prevention is key! Do not allow pets to have access to open water sources that have visible cyanobacteria (algae), which tend to discolor the water giving it a green paint or “green pea soup” appearance 2. There are some safe and alternative options for dogs that enjoy swimming or playing in water. Provide and offer clean water that is maintained in “kiddie pools”, tanks or containers, for wildlife and domestic animals to use 1.



  1. Bischoff, K. (2021) Algal Poisoning of Animals. Cornell University. Retrieved from https://www.merckvetmanual.com/toxicology/algal-poisoning/algal-poisoning-of-animals?query=blue%20green%20algae
  2. Gwaltney-Brant, S. (2019) Cyanobacterial Hepatotoxicosis (Canine). Veterinary Information Network, Inc. Retrieved from https://www.vin.com/members/cms/project/defaultadv1.aspx?pid=607&id=9272779
  3. Radke, S. (2022) Lecture 21: Water Quality and Cyanobacteria. Iowa State University College of Veterinary Medicine. Retrieved from https://canvas.iastate.edu/courses/86829/files/18052854?module_item_id=4373798

Written by:

Al Feinberg

Iowa State Veterinary Student Extern, Class of 2023