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From time to time we experience Blue Green Algae, or BGA, in our reservoirs and catchments that can affect drinking water.

Blue-green algae (BGA) is the common name for a group of algae with similar characteristics. When they encounter the right combination of conditions in a body of water they can multiply rapidly. These conditions are:

  • Still water that is clear enough for light to penetrate;
  • Warm temperature;
  • Adequate nutrients including phosphorous and nitrogen in the water;
  • When the mass of algae float to the surface, a vivid green bloom can appear overnight.

What are the signs to look for?

A sudden change in water colour overnight due to the appearance of a mass of vivid green algae (scum) floating to the surface of the water;

  • Scums can be green, blue-green or khakigreen, and can turn brown/green or white once dying off;
  • Scums may appear at dusk or dawn and disappear during the day;
  • There may be a strong earthy smell, or if the bloom is breaking down it may produce a strong rotting smell.

Why is it a problem?

Some species of blue-green algae in large numbers or ‘blooms’ can produce toxins and can have serious health implications for humans, animals and birds drinking or coming into contact with the water. While not all
blooms are toxic, they should be treated as toxic until the water has been tested.

Typical symptoms for people who have ingested water contaminated with blue-green algae include gastroenteritis, diarrhoea and vomiting.

Avoid all contact, including skin contact, with blue-green algae. Livestock are also at risk of poisoning by blue green
algae unless alternative drinking water supplies are provided, although livestock deaths are relatively rare. Livestock productivity will be reduced with milder cases of algae poisoning.


Last updated on 06 Oct 2023
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