Cyanobacteria Blue green algal bloom.
Blue-Green Algae Safety

Do You Have an Outbreak of Blue-Green Algae?

The main cause of concern about blue-green algae (cyanobacteria) is the ability of some to produce highly potent toxins. Whilst not all blue-green algal species are toxic, many are. With even different strains of the same species differing, it is important to play it safe. Some species are highly toxic, and visibly it is almost impossible to tell them apart from the non-toxic varieties.

Importantly though, blue-green algae contain lipopolysaccharides which act as contact irritants. Even if the other more potent blue-green algal toxins are not present, the presence of these contact irritants may make the water unsuitable for body contact or recreation. If the blue-green algae are present in bloom proportions the water should generally be considered unsafe.

Algae toxins

It is important to note that the toxins associated with blue-green algae are a by-product of their lifecycle processes. This means that the toxins themselves can persist long after the algae are removed.

Treating a water body with an algaecide such as Coptrol will kill the algae but the toxins will remain at dangerous levels for up to a month. For this reason, it is recommended that water treatment take place as soon as possible after the algal bloom is recognised. Leaving the bloom to grow without taking quick action will result in the toxicity levels continuing to increase.

Algal blooms

If a body of water is affected by a cyanobacteria algal bloom it is vital to keep all animals away, whether household pets or livestock.

Ensure that humans or animals do not:

  • Drink the water.
  • Eat mats of dried algae left along the shoreline.
  • Drink the water treated to kill blue-green algae for at least a month, because dead or ruptured cells of cyanobacteria release poisonous toxins.
  • Drink from the scum left along the shoreline because the scum is especially toxic.

If any of your animals (or people) have been in the vicinity of water infested by algae, be on the lookout for potential poisoning. Moreso, correct recognition of these symptoms can help alert you to the fact that you may have an algae problem.

Symptoms of algae poisoning

There are no known antidotes to cyanobacterial poisoning. It is possible, however, to prevent further absorption of the toxins into the system if treatment is provided soon enough.

Animals can exhibit a variety of symptoms, the most common being:

  • Muscle weakness
  • Lethargy
  • Reduced appetite or off their feed
  • Paleness
  • Mental derangement
  • Diarrhea
  • Photosensitivity
  • Spontaneous abortion

Whilst it is extremely rare for humans to be seriously poisoned, it is much more common with animals. Serious cases of algae poisoning will cause distress and animals may suffer muscle tremors and potentially die within a few hours or days.

Blue-green algae safety checklist

To help you manage potential outbreaks of cyanobacteria algae we’ve put together this checklist.


  • Regard blooms as toxic until water is tested.
  • Avoid skin contact; wear rubber gloves when collecting samples.
  • Inspect all dams, ponds, and troughs regularly in hot weather.
  • Isolate all people and stock from affected areas.
  • Make sure an alternative drinking water supply is available to stock. 
  • Contact a veterinarian if animals show symptoms of poisoning. There are no effective antidotes to cyanobacterial poisoning, but it is possible to prevent absorption of the toxin, provided the vet is called quickly after ingestion.
  • Treat the water body as soon as possible with an effective algaecide.

Do not:

  • Drink or swim in it.
  • Rinse feedstuffs in it.
  • Eat fish, shellfish, etc. caught in affected water.
  • Spray or irrigate crops with it.
  • Use water that has blue-green algae in it on plants being grown for human consumption, particularly for spray-irrigated salad and leafy vegetables. Dried algal cells on the leaves can remain toxic for several months.

Important notes:

  • U.V. light does not degrade blue-green algae toxins.
  • Use of biocidal chlorine does not degrade the toxins.
  • Boiling algal water will not make it safe.
  • Algaecides used to kill blue-green algae do not kill the toxins in the algae.

Blue-green algae toxins are colourless, odourless, and remain toxic for at least 3-4 weeks. They will eventually degrade through normal microbial activity.

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