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Blue-green algal poisoning

Also known as cyanobacteria


Potentially toxic cyanobacteria, or blue-green algae, may form dense blooms in fresh water bodies. This may be seen as a thick green coat or scum within the upper water layer and surface.  Blooms are mainly a problem in late summer and autumn.  They are associated with nutrient over-enrichment due to factors such as animals defecating and urinating in the water or fertiliser run-off.  Many blooms are not toxic, but all should be considered potentially so.  A range of cyanobacterial genera and species have been described including Microcystis aeruginosa and Anabaena circinalis.  Different cyanobacteria may produce hepatoxins and/or neurotoxins.

Affected animals may be found dead. Clinical signs due to neurotoxins may include: muscle tremor, staggering, salivation, hyperaesthesia, diarrhoea and recumbency. Clinical signs due to hepatotoxins may include: anorexia, dehydration, jaundice, hypersensitivity or stupor, photosensitivity and recumbency.

Diagnosis and tests available


Diagnosis is based on the visible presence of an algal bloom in animals’ drinking water confirmed by microscopic examination for blue green algae.

Test available


Sample(s) required

Days of the week test is conducted

Turnaround time1

Histopathology examination

Fixed tissue

Monday – Friday

Up to 5 days

Microscopic examination for blue-green algae

Water and scum



1 Turnaround times are provided as a guide only. For specific information about your submission please contact Customer Service.

Specimen requirements

Fixed tissue
  • Liver and kidney
  • Submit fixed in neutral buffered formalin at a 10:1 ratio of formalin:tissue
Water and scum
  • 100 ml
  • Submit chilled in a leak proof container

Further information

NSW DPI general information on blue-green algae.


Microscopic confirmation of the presence of cyanobacteria indicates the possibility of cyanobacterial poisoning, but does not confirm that the bloom is toxic.