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Health Warning Reminder – Change of Dominant Cyanobacteria (Algal Bloom) Species in Lake Ellesmere (Te Waihora)

Tuesday 17 November 2020Media release3 minutes to read

Health warning  – algal bloom in Lake Pegasus

A health warning remains in place for Lake Ellesmere

Canterbury District Health Board’s Community and Public Health unit has been advised by Environment Canterbury that the dominant species of potentially toxic blue-green algae (planktonic cyanobacteria) found in Lake Ellesmere (Te Waihora) has changed from the initial health warning that has remained in place since 24 December 2017.

The type of cyanobacteria that are currently present in high concentrations are:

  1. a) Nodularia which can appear as a thick surface scum or be suspended throughout the water.
  2. b) Dolichospermum (formerly called Anabaena) which can be present as green globules floating in the water column or form surface scums or sheens.

People should avoid the lake and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.

Dr Cheryl Brunton, Canterbury Medical Officer of Health, says the algal bloom can produce toxins harmful to humans and animals; people should avoid contact with the water until further notice.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips. If you experience any of these symptoms visit your doctor immediately and please let your doctor know if you have had contact with the lake water.

“No one should drink the water from the lake at any time. Boiling the water does not remove the toxin,” Dr Brunton says.

Animals that show signs of illness after coming into contact with algal mats or scums should be taken to a vet immediately.

Fish and shellfish can concentrate toxins and their consumption should be avoided. If fish are eaten, remove the gut and liver and wash in clean water.

Further information on gathering Mahinga Kai can be obtained below.

Environment Canterbury monitors the lake weekly at Lakeside Domain during summer and the public will be advised of any changes in water quality that are of public health significance.

Facts about cyanobacteria:

  • Cyanobacteria occur naturally but can increase rapidly during warmer months.
  • Algal blooms are caused by a combination of nutrients in the water (such as nitrogen and phosphorus), and favourable weather conditions (e.g. increased temperature, calm days).
  • If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.
  • Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.
  • Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g. wind). If a health warning is in place avoid contact with the water.

For further details visit:

Or contact Community and Public Health on (03) 364 1777:

For more information about Mahinga Kai:



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Page last updated: 17 November 2020

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