Harmful algae Guide
Harmful algal blooms (also referred to as 'phytoplankton blooms', 'microalgal blooms', 'toxic algae' or 'red tides') are common seasonal events in both fresh and coastal marine waters throughout Queensland.
Algal blooms caused by organisms may pose a direct threat to human and animal health, and can have:
- economic impacts (e.g. increased cost of treating the water supply or the need to use alternative supplies)
- social impacts (e.g. disrupted recreational use of waterways)
- environmental effects on aquatic ecosystems.
Queensland government response plan
To reduce the risk to human and animal health and to support a coordinated multi-agency response, the Queensland harmful algal bloom response plan was developed. This response plan is supported by the Queensland harmful algal bloom operational procedures.
Both the response plan and the operational procedures are under review; however, this guide provides information about algal blooms and contacts to report outbreaks.
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Blue-green algae in freshwater
Despite their name, blue-green algae are actually types of bacteria known as Cyanobacteria.
Some species have the potential to produce toxins. This cannot be determined by ‘naked eye’ inspection; only a laboratory analysis can verify the potential for toxicity.
Immediate action
If you suspect that blue-green algae have infested a water source used for drinking, stock watering or domestic purposes, you should refrain from using that water until a suitably trained person has identified the algae.
Please note: boiling the water will not solve the problem.
Blue-green algal blooms
An algal bloom is a mass of algal cells which discolour the water, form scums, produce unpleasant tastes and odours, and seriously reduce the water quality.
Not all blue-green algal blooms are toxic. Those that are may change their toxicity slowly over a period of weeks to months.
Blue-green algal blooms often persist for several weeks, depending mainly on the weather or flow conditions. Cooler, windy weather or increased flow may reduce or prevent blooms from occurring.
As the bloom dies, the cells tend to become 'leaky'. If the bloom contains species that produce toxins, these will be released into the surrounding water. Once released, some toxins may persist for more than three months before sunlight and the natural population of bacteria in the water degrade them.
Related information
- Lyngbya monitoring (for coastal and estuarine blooms)
- Healthy land and water
- Australian Institute of Marine Science (AIMS)
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Reporting outbreaks
A number of response agencies (state government, local governments and water storage operators) have jurisdiction over harmful algal blooms. The lead response agency depends on the type of water body and the threat posed.
Below is a summary of the agencies responsible for harmful algal bloom outbreaks:
Human health related water
Water bodies impacting on health of production animals
Department of Agriculture and Fisheries
Estuarine and marine waters
Department of Environment, Science and Innovation
Within protected areas
Department of Environment, Science and Innovation
For scientific advice
Department of Environment, Science and Innovation
Full details on response agencies and specific contacts can be found in the Queensland harmful algal bloom response plan and operational procedures.
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Health effects
Water contaminated by blue-green algae constitutes a health risk to humans.
Drinking water
Due to the toxins they may produce, blue-green algae can affect water consumers in a number of ways. They have been associated with nausea, headache, vomiting, abdominal pain, diarrhoea, gastroenteritis, muscle weakness, pneumonia and paralysis.
Note: Boiling the water will not destroy toxins. Boiling will kill algae but in doing so will release toxins into the water. In fact some toxins become more dangerous as a result of boiling the water.
Skin contact
Contact with blue-green algae (toxic and non-toxic forms) through water-based activities can cause problems such as
- skin rashes
- swollen lips
- eye irritation and redness
- ear ache and itchiness
- sore throat
- hayfever symptoms
- asthma
- and possibly promotion of skin tumours.
The risk of problems is likely to grow as contact time increases.
Eating fish from algae-affected waters
The identification of Paralytic Shellfish Poisoning (PSP) toxins in one of the species of blue-green algae in Australia has highlighted concerns about possible neurotoxin bioaccumulation in edible mussels and other shellfish.
In marine waters, consumption of shellfish contaminated by PSP has caused many human deaths. Cylindrospermopsin, another blue-green algal toxin common in Queensland freshwaters has been identified in the edible flesh of crayfish. Therefore, mussels, yabbies and other shellfish caught in algae infested waters should not be consumed.
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Livestock and farm dams
Livestock may be adversely affected through the following:
- if they drink water containing cyanobacterial cells
- eat mats of dried algae left along the shoreline
- drink water contaminated with toxins released from dead or ruptured cells.
Stock deaths have occurred after drinking contaminated water. As not all toxic algae produce blooms that are readily recognisable, it is important that all stock deaths and illness are reported to the Department of Agriculture and Fisheries.
If poisoning occurs, animals may exhibit a variety of symptoms. Typically these can include:
- muscle weakness
- lethargy
- reduced or no feeding
- paleness
- mental derangement
- diarrhoea.
In serious cases animals may suffer general distress, muscle tremors and coma upon which death follows within a few hours to a few days.
Where an alternative source is not available and the bloom is floating and localised, it may be possible to allow stock to drink from an area on the upwind side of the bloom.
Cyanobacteria are particularly hazardous when they accumulate as scums at the water’s edge and stock are at risk of drinking water with high concentrations of cyanobacterial cells.
Please note: it is not recommended to treat blooms with algicides or herbicides as they destroy the cyanobacterial cells, leading to a rapid release of toxins into the water. Algicides can also adversely affect fish, invertebrates, and aquatic plants.
What should you do?
The presence of a bloom does not necessarily mean that animals will be poisoned, so the following steps should be taken to assess the risk:
- Establish that animals are drinking the water or eating dried algae mats from the area where a bloom has been identified.
- Have a suitably qualified laboratory examine a sample of the water from the dam. They can identify the cyanobacteria in the bloom and determine whether they are present in numbers large enough to constitute a risk.
- Care should be taken to avoid direct contact with scums or suspect water while taking samples. Wear rubber gloves if taking samples and wash thoroughly with clean water following exposure.
- If necessary, the laboratory may advise you that it would be appropriate to identify and measure the toxins in the water.
Since all blooms of cyanobacteria have the potential to be toxic and all livestock are susceptible, it is prudent to consider all blooms toxic until proven safe. In the interim, stock should be withdrawn from the water supply and an alternative source used.
Harmful algae, 28 Aug 2023, [https://www.qldgovau.staging-services.qld.gov.au/environment/water/quality/algae]
This document is uncontrolled when printed. Before using the information in this document you should verify the current content on https://www.qldgovau.staging-services.qld.gov.au/environment/water/quality/algae.