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Peak algae season

December 2019

Blue green algae blooms

Blue green algae blooms occur commonly in the summer months, especially under drought conditions. Our team of District Veterinarians has been fielding questions about the effects on livestock over the last few months.

Blue green algae (cyanobacteria) are present normally in Australian waterways. Under the right conditions (warm temperatures and increased water levels of nitrogen and phosphates), visible algal blooms can form. Wind can cause the algae to accumulate at one side a water source, concentrating the toxins in that area.

Two types of toxins are produced by blue green algae. Hepatotoxins cause severe liver damage, and neurotoxins which affect the nervous system. Both can lead to sudden death, while the hepatotoxins can cause jaundice and photosensitisation at lower levels. The prognosis for animals with clinical signs of blue green algae toxicity is poor. There are no practical treatment options for livestock.

A diagnosis of blue green algae toxicity is based on evidence of access to blooms, post mortem examination and laboratory testing of liver and water samples.

Preventing stock from accessing water contaminated by blue green algal blooms is the best way to minimise the risk of blue green algae toxicity. Sensible precautions include fencing off dams, providing alternative water sources or moving pumps to avoid the bloom. 

Algicidal chemicals can kill the blue green algae, but this releases the toxins into the water and increases the risk to stock for some time. Adding bales of straw to the water has been recommended overseas, but there is no evidence that this works under Australian conditions. 

Blue green algae have been described as looking like “a green film on the water”, or, if collected into a jar as shaken, as “green paint flecks”. Water testing can identify the cyanobactia, but testing for the toxins is difficult and expensive.

More information about prevention of algal blooms using alum and gypsum can be found here:
Farm water quality and treatment
Poisoning of Livestock

If you have concerns about livestock deaths your property, please contact a district veterinarian in your nearest office, or your private veterinarian.