So, your farm dam is turning green, it smells strange and it is the only water supply you have for the stock. Do you have toxic blue-green algae? Will the stock die? What are you going to do? Who do you contact for more help?

This page should give you the basic information you need to find out what the next step is that you need to take. The green dam may not be as dangerous as you think, but if it is, then you will need to take all precautions to ensure the safety of your stock and other water users.

What to do next - a step by step guide to what to do if you find blue-green algae.

Topic guide, this page.

So, you think you may have blue-green algae in your farm dam?


The tell-tale signs are:

Sudden appearance, or "bloom", of green, yellow, or beige colouring in the water, surface scums coloured green, blue, beige or white, strong chemical or vegetation odours, refusal by livestock, especially cattle and horses, to drink the water or signs of illness in stock.



The only sure way to identify blue-green algae is to have a trained person examine a water sample under a microscope.

What are blue-green algae?

Blue-green algae is the commonly used term for several types of photosynthetic bacteria (Cyanobacteria) that sometimes impart a blue-green tinge to water or form blue-green scums on the surface when present in large numbers. They are extremely small organisms visible under a high powered microscope as single cells, or clumps of cells. They need sunlight to grow.

What is a blue-green algal bloom ?

"Bloom" is commonly used to describe a rapid increase in algal numbers to a point where they discolour water, form scums produce odours and reduce water qulailty for human and livestock use .

Often, blue-green algal blooms occur because conditions suitable for their growth are created by human activities (towns, farming, industry) in the catchment of a farm dam, river or large public dam. These conditions include increased levels of phosphorus and nitrogen in the water, calm water behind weirs, in farm dams or in slow-flowing rivers, lack of fresh water inflows to rivers or dams, murkiness, removal of other vegetation that might compete for light and nutrients, chemicals toxic to organisms that eat algae, strong sunlight and high air and water temperatures.

Some blue-green algae have tiny gas bubbles in their cells allowing them to float to the surface for sunlight or sink to the bottom to feed. This explains why a bloom of blue-green algae can appear, disappear and reappear quickly even during a single day. Wind stirring also plays an important part in this process.


Dangers of blue-green algae

Aside from the aesthetic problem caused by their appearance, and their taints and odours, the worst feature of blue-green algae is their ability to produce poisons including neurotoxins and liver toxins.

The recorded effects of these toxins on humans and animals coming into contact with the water include allergic reactions and skin eye irritations. Gastroenteritis and liver damage may result if the water is taken into the body.

Each year in Australia , livestock deaths are reported due to the toxic effects of blue-green algae. Human deaths and illness have not been verified in Australia (although deaths have been reported in other countries), but evidence strongly suggests that the toxins are a hazard to human health.

Not all blue-green algal blooms are toxic, and toxicity may occur for only part of the time or in only part of the bloom. Blue-green algal blooms often persist for several weeks, sometimes months, depending mainly on the weather or water flow. Cooler, windy, cloudy weather or increased flows usually reduce or stop a bloom fairly quickly.

(Further details on algal toxicity.) Use a link not required hee as text.

What you can do - Immediate action

If you detect unpleasant odours or taints, observe surface scums or otherwise suspect that blue-green algae ~ have infected the water you use for drinking, cooking, kitchen uses, bathing and showering, swimming or livestock watering, you should stop using it until the algae have been identified by a trained person.

Where the presence of blue-green algae is suspected in dam water used for drinking or bathing, alternative water sources should be used. For households, these might include bore water or rain water tank storage. Carting water may be an effective short term alternative. Bottled water may be appropriate for drinking purposes for short periods.

Boiling will not deactivate algal toxins.

Physical filtration of blue-green algae will not remove toxins and must be followed by filtration through activated carbon if the water is for household use. Poisoning of blue-green algae with copper chemicals should not be carried out. Copper chemical treatments break open the algal cells, releasing toxins into the water and introduce an additional poisonous element to the water.

Activated carbon is a processed form of charcoal. It adsorbs organic chemicals including those causing algal tastes, odours and toxic effects. Filtering water through fine sediment filters first will remove larger particles, increasing the life of the carbon filter. Carbon filtration systems can be obtained from manufacturers of water treatment equipment. The Department of Land & Water Conservation - Town Water Services Branch - (02) 9895 5949 - provides advice on water treatment for country towns.

Long-term action

Long-term strategies for prevention of blue-green algal blooms are being developed by government agencies. An important element of these strategies involves improving catchment management to reduce the amount of phosphorus washed into farm dams, creeks and rivers.

Vegetation filters offer some protection for farm dams (see separate RIVERWISE notes Filter Zones for Farm Dams and Buffer Zones along Rivers and Creeks). You should avoid using products like superphosphate near creeks and depressions that supply your dams.

Reduced livestock access to the immediate dam catchment and dam foreshore can also help. This may mean fencing off the dam and piping water to a trough outside the fenced area. This has the added advantage of drawing the water from a depth in the dam where algal concentrations are commonly lower than the surface waters.


Sampling and testing

To fiond out how to sample and what to do, go to the What to do next page .

In some areas Council Staff, Irrigation companies or the Department of Land and Water Conservation (DLWC) will be able to identify the algae type locally. If samples need to be sent to a DLWC laboratory for identification, a charge of about $35 (plus transport) is made for the service. If a cell count is also required, to determine the abundance of blue-green algae, the charge will be about $63 per sample (plus transport).

If you intend to have a cell count carried out, some knowledge of how to take a representative sample is required. It is recommended that you seek advice from DLWC regional water quality staff before collecting a sample; or have the sample taken by someone with water quality training.

Toxicity testing can be carried out at specialist laboratories. Various different toxicity testing techniques are now available at a cost of about $180 or more per sample, depending on the method used. The sample collection and preservation method is also important to ensure a meaningful result - so seek advice before collecting a sample for toxicity testing. In general it is reasonable to assume toxins are present where potentially toxic algae are found in abundance. Toxicity testing may be desirable where stock deaths or illness has occurred.

Further information

For more information about blue-green algae, water testing and water quality, contact your local office of the Department of Land & Water Conservation.

Notification of blue-green algal blooms

Regional Algal Coordinating Committees (RACCs) have been established in each region to coordinate action by government agencies, local government and catchment management committees, in the case of major blooms. Blooms in rivers or water bodies accessible to the public - particularly where they are used for stock and domestic water supply or recreation - should be reported to the RACC:

Barwon Region ( Tamworth ) (02) 6764 5900

Central West Region (Orange) (02) 6360 8278

Hunter Region ( Newcastle ) (02) 4929 4346

North Coast Region (Grafton) (02) 6640 2000

Murrumbidgee Region (Leeton) (02) 69530700

Murray Region (Albury) (02) 6043 0100

Sydney/South Coast Region ( Parramatta ) (02) 9895 6300

Sunraysia Region (Dareton) (03) 5027 4303

These notes are adapted from RIVERWISE – Advisory notes for Rural Landholders. Published by the Dept. of Land and Water Conservation.

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