Blue-green algae

Blue-green algae, also known scientifically as Cyanobacteria, are a group of photosynthetic bacteria. These accumulations are frequently referred to as 'blooms'.

Blooms are most often blue-green in colour but can also be:

  • blue
  • green
  • reddish-purple
  • brown.

Blue-green algae blooms are likely to occur more often when the water is warm and enriched with nutrients like phosphorus or nitrogen. Under certain conditions, blue-green algae can accumulate in thick layers at the surface or water's edge.

Impact on humans

It's possible for blue-green algae to cause illness in humans. The symptoms in humans include:

  • rashes
  • headaches
  • fevers
  • gastroenteritis
  • seizures
  • respiratory failure.

People may be exposed to these toxins:

  • through contact with the skin (for example, when swimming)
  • through inhalation of water containing toxins (for example, when close to irrigation sprays, motor boating or water skiing)
  • by swallowing contaminated water, or
  • by eating fruit, vegetables or leaves with blue-green algae surface contamination.

Impact on animals

Blue-green algae can also cause illness in animals, which most often come into contact with contaminated water from affected farm dams.

Download the fact sheet Blue-green algae: options for livestock drinking water (WORD - 115.0 KB) for more information.

Impact on your water supply

There are several steps that livestock producers can take to prepare for blue-green algae impacting and potentially cutting off a water supply.

Livestock farmers should consider:

  • developing a plan for managing the situation where water availability becomes limited
  • completing a stocktake of the quantity and quality of water currently available on-farm that will be toxin-free
  • calculating the water requirements for animals that may need to be provided water if current sources become toxic, and therefore how many days' supply is available
  • planning for additional on-farm storage should you need to quickly access alternative water supply
  • planning for how sufficient water will be provided to livestock in the medium-term, which may include additional reticulation systems, finding agistment or selling stock.

See Managing blue-green algae in farm water supplies for more information.

More information

We have calculators and fact sheets to assist producers calculate water availability and animal demand:

Other resources:

Or see these pages from the New South Wales Department of Primary Industries:

Download the fact sheet

Page last updated: 27 Dec 2023