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Health warning removed for algal bloom at Lake Clearwater, Ashburton

Wednesday 27 January 2021Media release2 minutes to read

THIS IS AN ARCHIVED PAGE. The advice and information contained in this page may not be current and it should only be used for historical reference purposes.
Health warning  – algal bloom in Lake Pegasus

The health warning issued for Lake Clearwater has been removed

Canterbury DHB’s Community and Public Health unit has lifted its algal bloom health warning issued for Lake Clearwater, Ashburton on 21 December 2020.

Recent water testing at Lake Clearwater show that the planktonic cyanobacteria (blue-green algae) currently found in the lake do not produce the common cyanobacteria toxins. The dominant cyanobacteria in Lake Clearwater has therefore been temporarily re-classified as non-toxic.

The total concentration of cyanobacteria in the Lake also presents a low risk to public health at current levels.

Canterbury Medical Officer of Health Dr Ramon Pink says Environment Canterbury’s sampling of Lake Clearwater will continue on a weekly basis to ensure the safety of the public.

“The public will be informed if testing shows that concentrations have increased and toxin-producing cyanobacteria occur and there is increased risk to public health again,” Dr Pink says.

Facts about cyanobacteria:

  • Cyanobacteria (also called blue green algae) occur naturally but can increase rapidly during warmer months.
  • Cyanobacteria 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.
  • If a warning is in place, people and animals should not drink the water from the lake at any time, even boiled water.
  • Exposure to a cyanobacterial bloom can 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 lake water when there is a health warning in place.

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Page last updated: 19 August 2021

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