Dangers and problems

Dangers and problems

Freshwater, estuarine and marine algae can impact on water quality, in some cases leading to health risks for people, stock, wildlife and domestic animals.

Freshwater algae

Water quality problems

The presence of blue–green algae may lead to water quality problems.

In drinking water supplies high numbers of blue–green algae may cause taste and odour problems. When the algae die, they can cause blockages in the filters used for water treatment. Blue–green algae also pose a challenge for water supply authorities, as some species are capable of producing  toxins. These toxins need to be removed from the water supply before it is supplied for domestic use and consumption, or an alternative supply sought.

The over growth of blue–green algae reduces the sunlight available to the other aquatic plants and may lead to their death. When aquatic plants and algae die, large amounts of oxygen are consumed as decomposition occurs. This decrease in available oxygen in the water can lead to the death of aquatic animals  such  as fish and can increase the release of nutrients and toxic chemicals from the sediments.

Risks to humans and animals

Blue–green algae can pose a risk to human health because of the toxins they produce. These toxins can damage the liver and neurological system of both humans and animals and in severe cases can cause death. The cell walls of all blue–green algae contain contact irritants which can cause  gastrointestinal,  skin, eye and respiratory irritations to humans and animals.

Toxins produced by blue–green algae

Toxins are compounds that have a harmful effect on other cells, tissues and organisms. In the natural environment, these toxins are generally contained within the blue–green algal cell but they are released into the water when the cell is damaged or dies.

Blue–green algal toxins can be divided into the following groups:

  • Hepatotoxins cause blood to collect in the liver causing circulatory shock and can lead to death by internal haemorrhaging.
  • Hepatotoxins can cause weakness, vomiting and diarrhoea.
  • Nodularin and microcystin are two types of hepatotoxins.
  • Nodularin is produced by the algal species Nodularia spumigena.
  • In NSW, microcystin is produced by Microcystis.
  • Microcystins can bioaccumulate in aquatic invertebrates such as mussels so aquatic animals caught from water where there is an algal bloom should not be eaten.
  • Neurotoxins interfere with the functioning of the nervous system and can cause death of humans and animals within minutes by causing paralysis of the respiratory muscles.
  • In NSW, a neurotoxin known as saxitoxin is produced by the blue-green alga Dolichospermum.
  • Marine dinoflagellates (red tides) produce saxitoxins (also known as paralytic shellfish poisons) which concentrate in shellfish and have been known to cause death in humans.
  • Cylindrospermopsin is a non-specific toxin that in NSW is produced by the blue-greenalgae Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum.
  • This toxin is a relatively slow acting toxin that damages most organs in the body including the liver.
  • When non–toxic species of blue-green algae are present at concentrations above 10 cubic mm per litre, the water may still pose a risk to recreational and domestic users as all blue–green algae have lipopolysachharides in their cell walls.
  • Lipopolysachharides are less toxic than hepatotoxins or neurotoxins but are significant in terms of water supply for drinking, showering and recreation.
  • Lipopolysachharides have been associated with outbreaks of gastroenteritis, skin and eye irritations and hayfever, in humans that have come into contact with algal blooms. Humans that contact Lipopolysachharides in the aerosol form (fine spray eg sprinkler) may suffer asthma, eczema, and blisters in the lining of the nose and mouth.


Sunday 03 July
2,614,900 ML
2,618,706 ML
8,668 ML
1,239 ML
89,916 ML
Sunday 03 July