Questions and Answers — Blue-Green Algae
What is blue-green algae?
Blue-green algae are simple aquatic bacteria that occur naturally in habitats such as rivers and lakes, favouring still water habitats such as dams that can facilitate their growth. Different species of blue-green algae vary considerably in shape, colour and size.
Bodies of water containing high numbers of blue-green algae pose a health risk to humans when used as domestic water supplies or for water-based recreation. As blue-green algae numbers increase so does the risk of adverse health impacts, hence it is important to monitor blue-green algae levels.
Blue-green algae in water storages may affect the health of persons coming into contact with the water. The recreation hazard varies according to the types and respective amounts of algae present within the storage at any time. It is advisable to check the current recreation hazard level before water-based recreational activities are undertaken. As the recreation hazard increases so does the risk of being adversely affected through these activities.
- Swimming, sailing, water skiing, diving or any other water activity involving body contact with the water may cause skin and eye irritation
- Dangerous algal toxins can accumulate in the internal organs of fish (Remove all internal organs of the fish before cooking or eating)
- Drinking or accidentally swallowing water directly from a water storage may result in illness
What do the 'Low', 'Moderate' and 'High' symbols for the blue-green algae mean?
The World Health Organisation (WHO) have established three hazard levels against which storage operators and water users can assess the danger posed by blue-green algae during primary contact water recreation activities (i.e. swimming, canoeing, water skiing etc.). The following values are based on the WHO guidelines for safe practice in managing bathing waters which may produce or contain cyanobacterial cells and/or toxins (Chorus & Bartram 1999):
Low hazard: < 20 000 cells/mL (< 2.5 mm3/L cell biovolume)
Moderate hazard: 20 000 – 100 000 cells/mL (2.5 – 12.5 mm3/L cell biovolume)
High hazard: > 100 000 cells/mL or cyanobacterial scum formation in bathing areas ( > 12.5 mm3/L cell biovolume)
Blue-green algae can cause irritation to any part of the body that is directly exposed to it. This irritation is usually in the form of a skin rash, eye irritation, or earache. The more blue-green algae that is present in the water, the greater the chance that some irritation will occur if you swim in the water.
The levels on the sign are an indication of this risk given the current levels of blue-green algae. If the blue-green algae indicator indicates a HIGH level, there is a high chance that the average person will suffer some form of irritation. Moderate levels are less likely to cause a problem than high levels, however a risk is still present. Low levels are unlikely to cause any health problems, however some people are more sensitive than others.
The levels do NOT reflect the suitability of the water for drinking.
World Health Organisation Standards.
How often do the blue-green algae (BGA) levels change?
The SunWater website is updated regularly and should be checked for level changes. Insufficient data exists to predict when levels will change, however it can generally be assumed that BGA levels will increase during the warmer months of the year.
Should I go swimming?
The choice of whether or not you swim in the storage is something only you can decide. Some people are more susceptible to irritation than others just as some people are more prone to allergies than others. Furthermore, some people are more willing to accept the risk than others. SunWater provides the recreation hazard levels to help you assess the risk, however only you can make the decision. Noticeable surface scums are also an indication of an increased risk of irritation and should be avoided.
How long will the blue-green algae be here for?
Blue-green algae are a natural part of the environment. A very small quantity of blue-green algae is present all the time, but when the weather patterns are right for them to grow they can multiply into potentially harmful numbers (commonly known as a ‘bloom’), and there is very little that can be done to stop them. It is difficult to estimate when blooms will occur and when they will die off, although numbers tend to increase during summer and high temperatures, and decrease during the winter.
Can I eat the fish/shellfish (e.g. redclaw) I catch from the storage?
Fish and shellfish caught in storages with insignificant numbers of the four (4) potentially toxic species should be edible.
Fish and crayfish should not be eaten from storages containing high levels of Anabaena circinalis, Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Aphanizomenon ovalisporum, which can produce toxins (a kind of poison) that are harmful to people if consumed. Fish/shellfish that are living in water containing these toxins can absorb the toxins into their internal organs such as the liver.
Previously it was thought that removing fish innards would render them safe to eat. However, recent research indicates the possibility of toxin accumulation in fish flesh. Children and the elderly should be considered more susceptible to toxin effects when assessing the risks.
Note that you may require a permit to fish under the Stocked Impoundment Permit (SIP) Scheme, available from small businesses in the vicinity of stocked dams. Please visit www.dpi.qld.gov.au/fishweb for further information.
Is it OK to drink water from the dam?
No. The only water you should consume is either water that has been treated for drinking by a council such as the supply to a house in a town, or rainwater. Untreated water from the dam is not suitable for drinking regardless of blue-green algae numbers. Boiling the water will not make it safe to drink.
How can I treat the water so that I can drink it?
Water treatment is a complex process requiring the application of chemicals, filtration, and other processes that cannot be completed without sufficient resources and training. SunWater recommends that you only drink water that has been supplied for drinking by a council, or rainwater. Boiling the water will not make it safe to drink.
Will blue-green algae in the water affect my crops?
There is no evidence to suggest that blue-green algae is absorbed by plants or that it will affect the growth of plants. Some research has been performed that suggests a small amount of toxin (a type of poison produced by some types of blue-green algae) may dry on the plant surface if water containing toxic blue-green algae is sprayed on the plant.
Will blue-green algae in the water affect my stock (cattle, horses, etc)?
Stock have a higher tolerance than humans, however toxins produced by some blue-green algae can cause harm to stock. Stock should be prevented from watering where algal scums are present. Blue-green algae levels in on-farm storages are likely to differ from those recorded in the SunWater storage.
I have algae in my farm dam, will it affect my stock?
The scum may not be algae, and if it is, it may not be producing toxins. Refer to the Yellow Pages for Analysts or Laboratories who can conduct ‘blue-green algae analyses’ and advise you if ‘toxin testing’ will be necessary (e.g. Queensland Health Scientific Services).
What are the environmental implications of blue-green algae outbreaks?
Blue-green algae occurs naturally in the environment. There has been little research conducted on the effects of blue-green algae on aquatic fauna, and where fish deaths have occurred during an algal bloom, it has been difficult to separate the effects of blue-green algal toxins and other potentially contributing factors such as low oxygen levels.
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