Facts about blue-green algae
Download this information as a PDF here.
What is blue-green algae?
Blue-green algae are naturally occurring bacteria in our waterways and storages. Hot weather and low slow flowing water provide peak conditions for algae levels to increase in our rivers, streams and channels.
Blue-green algae contain toxins that are harmful to humans and animals.
It is not known how long the blue-green algae will remain at high levels however; cool, cloudy and windy weather will help to reduce blue-green algae levels.
How is blue-green algae detected?
GMW tests water on a weekly basis during times of peak blooms.
Samples are sent to a laboratory, where the blue-green algae are identified and counted under a microscope.
As soon as it is detected, GMW issues alerts and advice through its website, hotline and the media.
Can blue-green algae be removed?
Blue-green algae are very small and GMW cannot remove them.
Chemicals that kill blue-green algae cannot be used in natural waterbodies due to their impact on other creatures that live in the water.
How do I find out if there is a warning?
Warnings can be found 24 hours a day on the GMW website at our blue-green algae page. You can also phone GMW’s blue-green algae hotline on 03 5826 3785.
Warning signs are also placed at major recreational areas.
The website and hotline will also be updated when levels decline and warning signs will be removed.
I can't see any algae, is it safe to go in?
Blue-green algae are very small and can be present in water at high levels even when there is no obvious change to the colour of water.
Avoid contact with water if you suspect that it contains blue-green algae and if you do not know, err on the side of caution.
To check for current blue-green algae warnings visit www.gmwater.com.au/bluegreenalgae-alert or phone the GMW blue-green algae hotline on 03 5826 3785.
What will happen if I go in water with high levels of blue-green algae?
The Department of Health and Human Services advises that blue-green algae contain toxins and you may experience skin rashes, itchiness; sore eyes, ears and nose; asthma; numbness of lips and limbs; nausea, vomiting or diarrhoea.
The public are being advised to avoid direct contact with water that contains high levels of blue-green algae.
If you experience symptoms you should seek immediate medical attention.
For more information visit the health.vic website.
You can also phone NURSE-ON-CALL on 1300 60 60 24.
Will boiling the water make it safe?
No. The toxins cannot be destroyed by boiling water.
Boiling the water bursts the blue-green algae cells and releases toxins into the water increasing the possibility of experiencing symptoms.
Can I go fishing or eat fish I catch?
If you’re near the water or on a boat you should take care to avoid direct contact with the water.
You should not eat any mussels, yabbies or crayfish from algae-affected areas.
For advice on eating fish from affected waters, visit the health.vic website.
Stock and Domestic use
Can I still use the water for domestic use?
Water supplied by GMW is not fit for any use that may involve human consumption, either directly or indirectly, without first being properly treated.
Human consumption includes showering, bathing, washing, cooking, ice making and drinking.
The Department of Health and Human Services has a brochure on Private Drinking Water Supplies that GMW recommends reading.
For more information visit the health.vic website.
What is the risk to animals?
GMW does not guarantee the quality of the water it supplies.
We recommend landowners find an alternative supply for domestic and stock. Alternative supply options include dam water, bore water, tank water or purchasing water from a water carter.
If there is a cost for obtaining an alternative source of water, this is at the water user’s expense.
If you do not have access to alternative water suply, advise that you keep a close eye on the health of your stock and animals.
For further advice phone the Department of Economic Development, Jobs, Transport and Resources on 13 61 86 or visit agriculture.vic.gov.au
Can I still use the water for irrigation?
GMW recommends alternative water supplies should be used for irrigation, where available.
GMW recommends a number of alternative supply options, including dam water, bore water or purchasing water from a water carter. If you do not have access to alternate water supply, GMW advises you to keep a close eye on the health of your stock and animals.
If water is used for irrigation then stock should be kept away from recently irrigated areas.
Some blue-green algae toxins will remain toxic in a dry form. Continued application of affected waters can lead to toxin build up on foliage and this residue could be harmful.
Water affected with blue-green algae should not be used to water edible plants.
For more information, visit agriculture.vic.gov.au
Is water safe if I lower my pump?
In reservoirs and other deep water storages, blue-green algae levels can vary according to the depth of the water, with lower levels of blue-green algae typically found as the depth increases.
Customers with suction lines into reservoirs and other deep water storages should ensure suction lines are as far as possible below the surface. Doing so will reduce, but not eliminate, the risk of pumping blue-green algae contaminated water.
The varying level of blue-green algae that occurs in deep water storages does not occur in irrigation channels, rivers, creeks and streams, because they are much shallower; therefore, they currently have high levels of blue-green algae at all depths.
Therefore, in irrigation channels, rivers, creeks and streams, warnings to avoid contact with water that contains high levels of blue-green algae apply to all depths
Latest alerts and advice: Visit the GMW blue-green algae page at or phone the blue-green algae hotline on 03 5826 3785. Updates are also available at emergency.vic.gov.au
Health information: Visit health.vic or phone NURSE-ON-CALL on 1300 60 60 24.
Agriculture and stock: Visit agriculture.vic.gov.au