Algal Blooms


  • What is an algal bloom?
  • Problems with blue-green algae.
  • What to do if you have blue-green algae.
  • Farm Dams

Current Algal Alert Levels

What is an algal bloom?

Under favourable environmental conditions, blue-green algae may increase in numbers rapidly, causing population explosions, called blooms. When numbers of blue-green algae are at bloom level their noxious properties can cause problems for a range of water users. Algal blooms are unsightly and create an unpleasant odour. More importantly, the toxins of some species can cause sickness in humans and death or illness in stock or pets.

MRACC identify the presence of a bloom as the circumstances when the numbers of potentially toxic blue-green algae are high enough to pose a threat to :

  • Public health – when water may be used for consumptive (drinking) and domestic purposes.
  • Public health – when a natural water body may be used for recreation.
  • Stock – where the water supply is a natural body (this does not include private dams).

Photograph courtesy of NSW, DLWC publication “What Scum is That?”

Problems with blue-green algae

At low concentrations, blue-green algae cause no problems and are part of the natural water environment. In Australia , no human deaths have been directly attributed to blue-green algae although many stock deaths have been reported. At high concentrations of blue-green algae the following problems may be encountered:

•  Some toxins affect the skin and sensitive membranes. Other toxins affect the liver and may make a person more susceptible to other diseases. Children and those with liver problems may be more at risk. Neurotoxins affect the nervous system. In humans skin and eye irritation, dermatitis, gastroenteritis, diarrhoea and vomiting, nausia and headaches may occur.

•  Stock and wildlife may suffer skin sensitisation, paralysis, convulsions, liver damage, disorientation, constipation, scours, abortion or even death.

•  Foul taste and odour to the water.

•  Blocking of filters and sprinklers.

•  Water treatment processes due to chemical changes in the water.

•  Fish and other aquatic organism health due to extreme day/night fluctuations in water dissolved oxygen and pH.

What to do if you have blue-green algae

It is important to act quickly if you suspect that you have blue-green algae. Until you have a positive identification (or otherwise), treat the situation as potentially a full High Alert blue-green bloom.

1. Follow The quick 7 step guide2. What to do Next – Detailed information on what to do if you find blue-green algae in your water supply. Who to contact, how to take a water sample, where to send it etc.

The Quick 7 Step guide to dealing with algal blooms

Step 1 – Positively identify the algae/scum. 1. Use the QUICK ID TEST or 2. Detailed ID Test. 3. Contact a DLWC water quality officer for details on how to get the algae identified.

Step 2 – Use an alternative safe drinking water supply for humans and animals.

Step 3 – Avoid human and animal contact with water.

Step 4 – Report blue-green algae in public waterways to DLWC or your local council. Report blue-green algae in farm dams to the Dept. of NSW Agriculture.

Step 5 – Prior to treatment of any water supply contact DLWC.

Step 6 – Continue to monitor the state of the bloom and respond to any Algal Alerts.

Step 7 – Do not use any water until confident it is safe to do so.

Safe Drinking Water supplies

  • Use bore or rain water where available.
  • Once a bloom has started only use water from the contaminated source after FILTRATION through ACTIVATED CARBON.
  • Algicides are not recommended as they may cause the release of more toxins by breaking the algal cells down. Algicides may be damaging to the environment if used in rivers, creeks, lakes or any other water body.

Water treatment Information