Blue-green algae (BGA) are simple aquatic bacteria (cyanobacteria) that occur naturally in waterways such as creeks, rivers and still water habitats, such as dams.
Blue-green algae is always present, but when weather conditions are right for them to grow they can multiply into an algae ‘bloom’. It’s difficult to estimate when blooms will occur and when they will die off, although blue-green algae numbers tend to increase during summer and high temperatures. Untreated river or lake water should not be used for consumption, as boiling water does not remove toxins which may be produced by blue-green algae.
Bodies of water containing high numbers of blue-green algae may pose a health risk to humans when used for water-based recreation, such as swimming or water skiing. As blue-green algae numbers increase, so can the risk of adverse health impacts, so it is important to monitor blue-green algae levels.
The recreation hazard varies according to the types and respective amounts of algae present within the storage at any time.
For more information on blue-green algae, visit Water Quality Australia.
BGA – What it Means to your Water SupplyDownload
Blue-green algae levels
The National Health and Medical Research Council (NHMRC)’s Guidelines for Managing Risks in Recreational Water outlines three hazard levels for storage operators and water users to assess the risk posed by blue-green algae during primary contact water recreation activities (i.e. swimming, canoeing, water skiing etc):
≥500 to <5000 cells/mL Microcystis aeruginosa or biovolume equivalent of >0.04 to <0.4 mm³/L for the combined total of all cyanobacteria.
|≥5000 to <50 000 cells/mL Microcystis aeruginosa or biovolume equivalent of ≥0.4 to <4 mm³/L for the combined total of all cyanobacteria where a known toxin producer is dominant in the total biovolume. |
≥0.4 to <10mm³/L for the combined total of all cyanobacteria where known toxin producers are not present.
Level 1 guideline:
≥10 μg/L total microcystins.
≥50 000 cells/mL toxic Microcystis aeruginosa or biovolume equivalent of ≥4 mm³/L for the combined total of all cyanobacteria where a known toxin producer is dominant in the total biovolume.
Level 2 guideline:
≥10 mm³/L for total biovolume of all cyanobacterial material where known toxins are not present.
cyanobacterial scums are consistently present.
Sunwater monitors and updates blue-green algae hazard levels for its water storages, as per the NHMRC guideline and in accordance with Department of Natural Resources, Mines and Energy (DNRME) requirements.
For further information about the guideline and blue-green algae hazard levels visit the NHMRC website.
To view Blue-green algae levels, select a dam, weir or storage below: