Blue Green Algae: What to look for

Freshwater blue-green algal blooms can be recognised by:

  • discolouration of the water, by scum on the water surface, or
  • by an earthy or musty odour coming from the water.

However, toxic algae can only be positively identified by trained personnel.

If you suspect that there is a blue-green algal bloom in a water body, you should contact either the local council or the management authority for the water body or your local RACC.
RACCs should be alerted of any high blue-green algae counts.

Algae, a diverse group of mostly aquatic plants, can be found in both salt water and fresh water. The freshwater forms tend to be small, the vast majority being microscopic, although they often betray their presence by discolouring water.

Most algae are harmless to humans and animals but a few are highly toxic, particularly some of the blue-greens which actually resemble bacteria more closely than the true algae.

For convenience, all the freshwater algae can be grouped into four main categories:

  • Flagellates can swim independently and in large numbers can often affect the taste and odour of drinking waters.
  • Diatoms are usually brown or yellow in colour and are mostly free floating, while some types often attach to the stems and leaves of other water plants, coating them with a brown slime.
  • Green algae, which come in all shapes and sizes, are commonly present in reservoirs and dams, rivers and channels, on the sides of tanks and drinking troughs and in thick, tangled masses in low-lying swampy areas. They are not usually toxic but can clog filters, meters, valves and trickle irrigation lines.
  • Blue-green (cyanobacteria) algae can range in colour from yellow to purple. Some types can be highly toxic to humans, livestock and birds. They are capable of very sudden, explosive growth and may appear as a thick, smelly, green, paint-like scum on the surface of a lake or dam, particularly around the shallow edges, down wind, either in clumps or as filaments.

Characteristics of Blue-Green Algae

Outbreaks of blue-green algae often give off a characteristic musty odour.

Blooms can vary in appearance from pale to bright fluorescent green and may appear paint-like or granular in texture.

Blue-green algae outbreaks are generally confined to areas of still water with little turbulence.

Natural Occurrence of blue green algae in the environment

Blue-green algae (cyanobacteria) are an important, naturally occurring component of aquatic ecosystems and provide the primary food source to more complex organisms in the food chain.

In response to favourable environmental conditions, they may undergo spectacular population explosions, called blooms, which may be toxic to a wide range of aquatic and terrestrial organisms.

Blooms occurred under natural conditions, prior to the development of inland Australia and to river regulation. In 1830, explorer Charles Sturt noted that the waters of the Darling River had a taste of vegetable decay as well as a slight tinge of green. This note may well have been describing a blue-green algal bloom.

Regional Incidence of blue green algae blooms

Over the past 25 years, toxic and non-toxic algal blooms within water storages, weir pools and the inland rivers network of New South Wales, Victoria and South Australia, have been reported with increasing regularity.

In the Sunraysia Region of New South Wales and Victoria, significant algae blooms have been identified and monitored in recent years.

Typically, blue-green algae blooms affect many of the tributaries, backwaters and slower moving reaches of the River Murray during the warmer months from November to May.