retriever looking at a river

Toxic Algae or Cyanobacterial Toxicosis 

Algae is present in many of New Zealand’s lakes and rivers all year round, and is found across a range of water qualities (including high quality). In periods of warm weather and low water flow, toxic species of algae can outgrow non-toxic, species. Levels can change dramatically from one day to the next and aren’t necessarily consistent in all parts of rivers and streams.  It can also occur in stagnant water such as bird baths or small ponds/puddles.

Blue-green toxic algae (also known as cyanobacteria) is identifiable by a strong musty smell and presents as slimy brown/black mats in rivers and streams when wet, and light brown/white mats when dry. It can form films or scums on the water surface under the right conditions, sometimes giving lakes a vivid green colour. Its colour can vary from green to red and sometimes can just show a murky foamy scum on the water. Whether it is wet or dry, the algae is harmful when ingested. 

Cyanobacterial toxicosis is an acute, often fatal condition caused by toxins generated by cyanobacteria. Severe illness has been documented in people, livestock, wildlife, birds, dogs, fish, and other aquatic animals. 

Symptoms of toxic algae poisoning in animals include:

  • lethargy
  • vomiting
  • diarrhoea
  • muscle tremors
  • fast breathing
  • paralysis
  • convulsions.

In extreme cases, death can occur within 30 minutes after signs first appear. Some animals may collapse and die, with no other noticeable signs. Those animals that survive the early phase may then develop signs of liver failure (weakness, yellowing of the gums or whites of the eyes, depression, collapse, seizures, and trouble breathing).

There is no specific therapy, especially in cases with rapid onset of clinical signs. Immediate supportive care to treat seizures and shock (including intravenous fluids and anticonvulsant therapy) is needed as well as monitoring of vital signs, liver and kidney values, and clotting factors. Prognosis is generally guarded to poor, and many animals succumb before they can be presented for veterinary care. 

It is also important to note that for many intoxications, the laboratory diagnosis relies on detecting the toxin. To detect a toxin, the laboratory must know what to analyse for. Unlike in some forensic TV shows, there is no ‘machine’ capable of analysing a sample to determine a toxin as we don’t have analyses for all toxins.

It is important that dogs are not allowed to swim, wade in, or drink water that has visible cyanobacteria in it. However, it is impossible to tell just by appearance whether the water contains cyanobacterial toxins. Check your regional council website for current warnings on the toxic algae risk at popular rivers and lakes in your area.

If in doubt keep your pet away from waterways and contact your local vet clinic if you think your pet may have been exposed to the algae; even if it is out-of-hours, a duty veterinarian will be available to help you.