Blue-green algae (cyanobacteria)

Cause

The most common toxic blue-green algae in Queensland fresh waters are:

• Cylindrospermopsis raciborskii
• Microcystis aeruginosa
• Anabaena circinalis.

Description

An algal bloom refers to an accumulation of algae that can result in discolouration of water, surface scums, and unpleasant tastes and odours. Blooms can vary in colour, and may be easily seen on the surface or evenly spread throughout the water. They are most likely to occur when weather conditions are warm and nutrients in the water are abundant. Livestock, pets and wild animals can be poisoned by the toxins produced by some algal blooms.

Where the disease occurs

Algal bloom development can occur wherever lakes, reservoirs, dams and creeks have stagnant water. Cases of toxicity in livestock have occurred throughout Queensland.

Pets may also be affected. Dogs are particularly susceptible because they lick their coats after swimming.

In animals

Animals may die within minutes of clinical signs appearing, but can survive for several hours or up to 2 or more days after drinking a fatal dose. They can show muscle weakness, trembling, salivation, staggering, sensitivity to touch, convulsions, colic and diarrhoea.

Control of the disease

Algal toxicity has no effective antidote. Livestock should be prevented from drinking contaminated water. It may be necessary to move them to another paddock where they can access safe drinking water.

If animals have recently consumed contaminated water, it may help to drench them with activated charcoal or bentonite to try to prevent toxin absorption. However, this treatment is very expensive.

If you suspect that your animals may be at risk from an algal bloom, contact us. Early intervention methods may prevent stock losses, so it is important to contact us as soon as you suspect an algal bloom. The presence of toxic algae can be confirmed through the testing of water samples.

In the longer term, you can prevent algal blooms by reducing the amount of nutrients and sediments entering a dam or other water supply. You can achieve this by controlling stock access to dams to prevent bank erosion, high nitrogen levels in the water and the loss of aquatic plants. Fencing off the dam completely, planting local native water plants around the edges of the water and piping the water to troughs is the most effective way to reduce the incidence of algal toxicity in livestock.

In people

People become affected by drinking contaminated water or engaging in water sports, such as swimming or waterskiing, in water affected by an algal bloom.

Prevention

You can prevent the disease by avoiding any risk of skin contact with sources of contaminated water. Additionally, drink only bottled or rainwater.

Long-term prevention depends on reducing the nutrient concentrations in streams and storage. Techniques to treat or detoxify contaminated water, such as chlorination or filtering through activated carbon, may be undertaken.