Veterinary advice should be sought from your local veterinarian before applying any treatment or vaccine. Not sure who to use? Look up veterinarians who specialize in poultry using our directory listing. Find me a Vet

Algae Poisoning

Other Names: Cyanobacteria Poisoning, Blue-green Algae Poisoning

Cyanobacteria (also known as blue-green algae) produce toxins which can be deadly to chickens if ingested in large amounts. It can grow in any stagnant water source, such as poultry waterers, water troughs, buckets, ponds, lakes, baby pools, etc. Blue-green algae is more likely to grow rapidly when the stagnant water source is exposed to high temperatures, sunshine, and any sort of organic matter or debris.

The algae forms in large colonies that appear as scum on or just below the water source. The presence of bacteria often may be determined by a bluish tinge to the water. Concentrations of bacteria often are bluish green but may vary from dark green to brownish green, depending on the total bacterial population. In lakes and ponds, proliferation of blue‐green algae may result in a “bloom”, which is a build-up of algae that creates a green, blue-green, white, or brown coloring on the surface of the water, sometimes occurring as mats or scum. It may look like a floating layer of paint.

Cyanobacteria can produce two types of toxins, microcystins and anatoxins. Microcystins (hepatotoxins) affect the liver and anatoxins (neurotoxins) target the nervous system. The toxins enter the chicken’s body when they drink the affected water. The clinical signs of poisoning depend on which toxin is involved.

Hepatotoxins can severely damage the liver leading to organ failure, which can occur quickly or over several days. Clinical signs of exposure to the hepatotoxin may non-specific such as lethargy, loss of appetite, weakness, and pale comb, along with diarrhea and bloody or dark droppings.

When neurotoxins are ingested, signs of poisoning occur within 30-60 minutes of ingestion and death within minutes to hours after exposure. Since neurotoxins target the nervous system, signs such as muscle tremors, paralysis, and seizures may occur. Decreased oxygen delivery makes it difficult for the bird to breath, and causes the chicken’s comb to change to a crimson to purple color.

If chickens are suspected of having been exposed to blue-green algae, a veterinarian should be contacted immediately. If caught before signs occur, administering activated charcoal orally may help absorb the toxin.

Clinical Signs

Difficulty breathing
Loss of appetite
Weakness or inability to walk
Pale or purple comb
Diarrhea with dark, tarry droppings
Muscle tremors
Sudden death


  • History
  • Water testing for detection of algal toxins in water samples and GI contents


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Activated charcoal2.8 g/kg administered orally may help absorb the ingested toxins.K Marx



  • Provide fresh water sources in clean water containers.
  • Check all water sources at least twice a week.
  • Position water sources in shaded areas or reduce the amount of direct sunlight which will reduce algae growth, which need sunlight to survive and multiply.
  • Fence off or otherwise prevent access to stagnant, scum-covered ponds.
  • If a water source is treated with an algaecide such as copper sulfate, prevent birds from accessing the water for at least a week or longer to allow degradation of any released toxins in the water.
  • Purchase waterers which prevent birds from defecating in the water, such as nipple drinkers or water cups.



Scientific References

Risk Factors

  • Stagnant water sources
  • Not cleaning or checking waterers regularly
  • Water sources positioned in direct sunlight