Blue-green algae

GMW is responsible for the management of blue-green algal blooms within our storages, irrigation channels and drains. GMW regularly monitors and inspects a number of water bodies within our area of operation for blue-green algae.

Blue–green algae are naturally occurring bacteria that have the potential to be harmful as they can make people and animals sick.

Find out about current blue-green algae warnings here.

Algae awareness

Scums of blue-green algae in a lake
Scums of blue-green algae in a lake

Algae are a diverse group of mostly aquatic plants that can be found in both salt and fresh water. One type of algae, known as blue-green algae, has the potential to be harmful as they can make people and animals sick.

Blue-green algae are not plants but are actually photosynthetic bacteria. The technically correct term for them is cyanobacteria, however they almost always more commonly referred to as blue-green algae.

Not all algae are dangerous. There are many types of algae that can cause the water to change colour but are just harmless plants. The only way to tell if algae are harmful is to look at a water sample under a microscope.

To complicate things, high levels of blue–green algae do not always colour the water blue or green. The water can look yellow, brown, red, blue or green, or there may be no visible colour change at all.

An earthy, musty or sulphuric smell may accompany high levels of blue-green algae, however high levels of blue-green algae may be present when there is no obvious smell at all.

In low numbers, algae are not usually a problem and are in fact an essential part of a healthy body of water. Algae produce oxygen and are a source of food for many aquatic animals.

High levels of algae can affect water quality by causing peculiar tastes and odours, discolouration and unsightly scums. Algae can be a nuisance as they can be present on the sides of tanks and drinking troughs and may be in thick, tangled masses in low-lying swampy areas. Algae can also clog filters, meters, valves and trickle irrigation lines.

When algae is present in very high numbers, water quality can be severely affected as when they die the decaying algae may reduce the amount of oxygen dissolved in the water and cause aquatic animals to struggle to breathe and maybe even die.

When blue-green algae die they release toxins directly into the water. The toxins in blue-green algae can be poisonous to humans and animals.

Algae scums

Not all algae are dangerous. There are many types of algae that can be visible but are just harmless plants. The only way to tell is to look at a water sample under a microscope. As a precaution GMW recommends the public avoid any scums or discoloured water.

Scums can be reported to the GMW blue-green algae hotline on (03) 5826 3785.

Contributing factors to algae growth

Many factors can influence the growth of algae, including:

  • Weather: Long sunny warm days with no wind are most favourable for algae growth, although high levels of blue-green algae have been known to persist through winter. If there are high levels of algae is present, a few cloudy cold days may not significantly reduce blue-green algae levels.

  • Light: Algae need sunlight to grow and to make their own food. When the water is turbid (has a lot of soil/dirt in it) the algae can find it difficult to get the sunlight they need, therefore clear water is usually more favourable for algae growth.

  • Flow/turbulence: Still and stagnant water bodies are more favourable for algae growth as the algae are able to absorb the sunlight they need to grow.
    In large lakes stratification of water can occur, this usually means there is warm water in the top layer of lake and cold water at the bottom. The warm stagnant top layer is favourable for algae growth.
    High levels of blue-green algae may still be present in turbulent waterbodies with high flow as the algae may grow in stagnant areas and then be transported into the high flow turbulent areas. For instance, high levels of blue-green algae may be present in a fast flowing river, as the algae may grow in a stagnant lake and then be transported down the river.

  • Algae food (nutrient) levels: Many of our lakes and waterways have become enriched with algae food (nitrogen and phosphorus). This may have occurred naturally or as a result of human activities. The greater the levels of algae food, the greater the chance of algae growing in large numbers.

  • Algae predator numbers: Zooplankton, crustaceans, mussels, and aquatic insects eat algae. If water quality is impaired and these animals are reduced in numbers, the algae may grow in large numbers as there are fewer animals there to eat them.

These and other more complex factors operate in combination, and no one factor can be pinpointed as a cause of high levels of algae.

High levels of blue-green algae blooms can persist for two to three weeks, months and even an entire summer period if conditions are favourable.

Blue-green algae warnings

Low levels of blue-green algae are present in water all the time, however the Victorian government set a maximum level considered safe for human health. Warnings are issued when the level of blue-green algae exceeds safe levels.  It cannot be predicted how long a warning will remain in place.

Warnings can be found 24 hours a day on the GMW blue-green algae hotline, call (03) 5826 3785 and our blue-green algae warnings page. Both the hotline and website are updated as soon as new information is received.

Blue-green algae special features

There are hundreds of different types of blue-green algae. Some types of blue-green algae have special features that other algae just don’t have. These are:

  • Buoyancy: Some types of blue-green algae have gas vacuoles which enable them to change their position vertically in the water column.   They stay well below the surface most of the time, only rising to the surface in the middle of the day to get sunlight for food and growth. This is an advantage because they can avoid predators and find areas with higher food levels.

  • Gelatinous protection: Some blue-green algae have a jelly-like substance which surrounds their bodies. This helps them because blue-green algae predators are filter feeders; when the blue-green algae get eaten only the jelly gets digested, allowing the algae cells pass through unharmed.

  • Reproductive cells: Some blue-green algae have specialised reproductive cells which are larger than normal cells and are able to reproduce sexually. This enables the algae to grow considerably faster than normal algae. During times of drought these cells are also able to lay dormant in the soil for years, and are able to start reproducing quickly once water returns.

  • Phosphorus storage: Some blue-green algae are able to store phosphorus within their cells so that in times of low nutrient levels they have a store available to use.

  • Nitrogen fixation: Some blue-green algae are able fix nitrogen directly from the air; therefore in times of low nitrogen some blue-green algae are still able to grow when other algae can’t.

Blue-green algae toxins and symptoms

Direct skin contact with water containing high levels of blue-green algae through showering, bathing, swimming, water skiing and other recreational activities may result in a variety of symptoms. Advice on the health impacts of blue-green algae can be obtained from the Better Health Channel.

The symptoms experienced as a result of contacting or ingesting water containing these toxins can take up to a week to appear. If you experience symptoms you should seek medical attention.

Risk to livestock

Livestock including cattle, sheep and poultry may be affected as a result of drinking water contaminated with blue-green algae. Information on how blue-green algae can make animals sick may be obtained from Agriculture Victoria.

If you suspect that your animals are showing symptoms of contact with blue-green algae you should seek veterinary advice.

When there are high levels of blue-green algae present it is recommended that alternate water supplies be utilised.  Advice on the safety and suitability of alternative sources for on-farm use may be obtained from Agriculture Victoria.

Risk to edible plants

Advice on the use of blue-green algae contaminated water for edible plants may be obtained from Agriculture Victoria. When there are high levels of blue-green algae present it is recommended that alternate water supplies be utilised. Advice on the safety and suitability of alternative sources for on-farm use may be obtained from Agriculture Victoria.

Blue-green algae in farm dams or private farm channels

If you suspect you have blue-green algae in your farm dam advice on the management of blue-green algae blooms may be obtained from Agriculture Victoria by phoning 136 186 or visiting Agriculture Victoria.

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. Commercial systems for treating individual household water supplies are available and can be found by looking in the Water Treatment and Equipment section in the Yellow Pages.

The Department of Health and Human Services has a brochure on Private Drinking Water Supplies that GMW recommends reading. 

Alternative water supplies

When there are high levels of blue-green algae present it is recommended that you seek alternative water supplies.

Boiling the water will not make the water safe and may in fact increase the toxicity of the water. Boiling the water bursts the blue-green algae cells and release toxins directly into the water. The toxins are not able to be destroyed by boiling, therefore showering in or drinking untreated water will be unsafe.

Water supplied by G-MW 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.  Commercial systems for treating individual household water supplies are available and can be found by looking in the Water Treatment and Equipment section in the Yellow Pages or searching the internet.

The Victorian government has a brochure on Private Drinking Water Supplies that GMW recommends reading.

Individuals will have to determine the best options for their particular circumstances.  Options may include good quality bore water, carted water, bottled water or tank water.

Advice on the safety of alternative sources of drinking water supply may be obtained from local government environmental health officers.

Advice on the safety and suitability of alternative sources for on-farm use may be obtained from Agriculture Victoria.

Blue-green algae treatment options

At present, there are few options for the treatment of blue-green algae affected water.

Blue-green algae are very small and therefore they cannot be removed manually. 

Urban water authorities employ sophisticated treatment systems including expensive activated carbon treatment to treat drinking water supplies.

The chemicals that are able to kill blue-green algae cannot be used in natural waterbodies.

Commercially available systems for treating individual household drinking water supplies do exist, although these are not suitable for treating the large volumes of water needed for irrigation and livestock water supply.

Commercial systems for treating individual household water supplies can be found by looking in the Water Treatment and Equipment section in the Yellow Pages or searching the internet.