Blue-green algae - Frequently asked questions

Facts about blue-green algae

Download this information as a PDF here, opens in a new window.

What is blue-green algae?

Blue-green algae are naturally occurring bacteria in our waterways and storages. Hot weather and still water provide ideal 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.

How is blue-green algae detected?

Water sample are sent to a laboratory, where the blue‑green algae are identified and counted under a microscope.

When high levels are detected GMW issues alerts warnings 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?

Current warnings can be found on the GMW website at You can also phone GMW’s blue-green algae hotline on 03 5826 3785 anytime.

Warning signs are placed at major recreational areas.

When levels decline the website and hotline will be updated 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 or looks unusual.

To check for current blue-green algae warnings visit  or phone the GMW blue-green algae hotline on 03 5826 3785.

Human contact

What will happen if I go in water with high levels of blue-green algae?

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.

If you experience symptoms you should seek immediate medical attention.

People are advised to avoid direct contact with water that contains high levels of blue-green algae.

For more information visit

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, opens in a new window 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, opens in a new window website.

What is the risk to animals?

GMW does not guarantee the quality of the water it supplies.

Landowners are recommended to 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 alternate water supply, GMW advises you to keep a close watch on the health of your animals.

For further advice phone the Department of Economic Development, Jobs, Transport and Resources on 13 61 86 or visit, opens in a new window

Irrigation use

Can I still use the water for irrigation?

GMW recommends alternative water supplies should be used for irrigation, where available.

If water is used for irrigation then stock should be kept away from recently irrigated areas.

Water affected with blue-green algae should not be used to water or wash edible plants.

For more information, visit, opens in a new window

Is water safe if I lower my pump?

In reservoirs and other deep water storages, blue-green algae levels can vary with depth, with lower levels of blue-green algae typically found as the depth increases.

Customers with suction lines into deep water should ensure the foot valve is as far below the surface as possible. 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 usually occur in irrigation channels, rivers or creeks, because they are much shallower and better mixed. These waterbodies can have high levels of blue-green algae at all depths when a warning is present.

More information

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, opens in a new window

Health information: Visit health.vic, opens in a new window or phone NURSE-ON-CALL on 1300 60 60 24.

Agriculture and stock: Visit, opens in a new window