Blue-Green Algae

Blue-Green Algae

What are Blue-Green Algae?

Blue-Green Algae (BGA) or cyanobacteria are microscopic organisms found naturally in freshwater environments across Australia.

They have several traits that give them a competitive advantage in aquatic environments. Some species can:

  • fix atmospheric nitrogen allowing them to thrive in low-nutrient waters, survive in poor water quality conditions, and produce chemicals that suppress the growth of other algae
  • move vertically through the water to access light and nutrients, giving them an edge over microorganisms without this mobility.

In summer, warmer temperatures, sunlight and nutrient-rich water create the ideal conditions for BGA to multiply quickly, forming large blooms (In contrast, cooler temperatures and reduced light during winter often lead to a natural decline.)

While most cyanobacteria are harmless, some species produce toxins that can affect humans, animals and aquatic life. These toxins can contaminate drinking water, cause skin irritation and lead to health issues if ingested.

Blooms may appear as:

  • green, blue-algae or reddish-brown scum on the water surface
  • paint-like streaks or clumps
  • discoloured water with a musty or earthy smell.

It’s important to note that not all visible blooms are harmful. Some non-toxic algae can look like toxic cyanobacteria. This makes accurate identification and monitoring essential.

To help protect public health and enjoyment of our waterways, Sunwater actively monitors for BGA and provides timely updates to the public of any potential risks in addition to updating signage at Sunwater storages. However, BGA blooms can develop between scheduled monitoring.


If you see visible algae growth, surface scums or discoloured water, it is advised to take a precautionary approach. Avoid contact with the water and keep pets and livestock away.

How Sunwater monitors BGA

Sunwater actively monitors water quality across its storages to detect and manage cyanobacterial blooms. We regularly collect samples at each storage, which are sent to a laboratory to identify:

  • species and quantity present
  • if any toxic species are present and in what quantity
  • the hazard level at each storage.

Managing BGA

Managing BGA blooms presents several challenges:

  • Currently, there are no approved chemical treatments or large-scale solutions that can safely and effectively control BGA in major water storages.
  • The sheer size and depth of Sunwater’s storages make it impractical to treat blooms directly.
  • BGA growth is often driven by nutrient runoff (especially nitrogen and phosphorus) from upstream land use activities. Effective long-term management requires catchment-wide land and water management practices, which are outside Sunwater’s direct control.

Potential impacts

Health

You can be exposed to BGA through:

  • direct contact e.g. when swimming, paddling, waterskiing or jetskiing
  • inhalation white boating or fishing
  • drinking untreated water or eating impacted fish or crayfish.

Health effects may include:

  • skin rashes, eye irritation and hayfever-like symptoms
  • gastrointestinal issues such as vomiting, diarrhoea, fever, and headaches
  • respiratory symptoms from wind-blown scum
  • liver and kidney damage.
Irrigation and livestock

When present in large numbers, BGA can cause clogged pumps and filters and reduce water quality for crops and livestock.

Industrial

Water-dependent industries can be affected by large BGA blooms. They can cause water treatment filter and membrane fouling, which may affect system performance and increase the need for maintenance.

Environment

BGA blooms disrupt aquatic ecosystems by:

  • reducing oxygen levels during die-off
  • blocking sunlight to aquatic plants
  • releasing toxins
  • outcompeting native algae, which affects biodiversity and food webs.

Stay informed

Sunwater is committed to keeping the community informed about BGA risks. You can stay up to date by:

To view Blue-green algae levels, select a dam, weir or storage below: