Blue-Green Algae

Blue-Green Algae

Photo: Blue-green Algae on water surface

What is Blue-Green Algae?

Blue-green algae are a number of different species of a type of bacteria (known as cyanobacteria) with the ability to use the sun’s energy to make food in the same way that many plants do.  Under certain conditions blooms of algal growth can appear forming thick scums on the surface of the water. 

Why is it a Problem?

Effects on Humans and Animals

These are of concern to waterways users as one quarter of algal blooms are known to produce toxins. These toxins can result in illness in humans but have been known to kill cows, sheep and dogs that have been drinking from the water’s edge.

Humans face a health risk from exposure to blue-green algae toxins.  Illnesses including skin rashes, eye irritation, vomiting, diarrhoea, fever and muscle and joint pain have occurred in people who’ve swallowed or swam through algal scum. These haven’t led to long-term effects or death but, in some cases, the illnesses can be severe.


When the blooms decay they use up the oxygen in the water and can lead to the death of aquatic organisms and a decline in biodiversity.

Blooms have a negative impact on the appearance, quality and use of the water.

Reporting Invasives

You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.