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Harmful algae

Livestock and farm dams

Livestock may be adversely affected through the following:

  • if they drink water containing cyanobacterial cells
  • eat mats of dried algae left along the shoreline
  • drink water contaminated with toxins released from dead or ruptured cells.

Stock deaths have occurred after drinking contaminated water. As not all toxic algae produce blooms that are readily recognisable, it is important that all stock deaths and illness are reported to the Department of Agriculture and Fisheries.

If poisoning occurs, animals may exhibit a variety of symptoms. Typically these can include:

  • muscle weakness
  • lethargy
  • reduced or no feeding
  • paleness
  • mental derangement
  • diarrhoea.

In serious cases animals may suffer general distress, muscle tremors and coma upon which death follows within a few hours to a few days.

Where an alternative source is not available and the bloom is floating and localised, it may be possible to allow stock to drink from an area on the upwind side of the bloom.

Cyanobacteria are particularly hazardous when they accumulate as scums at the water’s edge and stock are at risk of drinking water with high concentrations of cyanobacterial cells.

Please note: it is not recommended to treat blooms with algicides or herbicides as they destroy the cyanobacterial cells, leading to a rapid release of toxins into the water. Algicides can also adversely affect fish, invertebrates, and aquatic plants.

What should you do?

The presence of a bloom does not necessarily mean that animals will be poisoned, so the following steps should be taken to assess the risk:

  • Establish that animals are drinking the water or eating dried algae mats from the area where a bloom has been identified.
  • Have a suitably qualified laboratory examine a sample of the water from the dam. They can identify the cyanobacteria in the bloom and determine whether they are present in numbers large enough to constitute a risk.
  • Care should be taken to avoid direct contact with scums or suspect water while taking samples. Wear rubber gloves if taking samples and wash thoroughly with clean water following exposure.
  • If necessary, the laboratory may advise you that it would be appropriate to identify and measure the toxins in the water.

Since all blooms of cyanobacteria have the potential to be toxic and all livestock are susceptible, it is prudent to consider all blooms toxic until proven safe. In the interim, stock should be withdrawn from the water supply and an alternative source used.

In this guide:

  1. Blue-green algae in freshwater
  2. Reporting outbreaks
  3. Health effects
  4. Livestock and farm dams

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