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Health warning removed for algal bloom in Hakatere/Ashburton River at SH1

Wednesday 17 March 2021Media release2 minutes to read

Health warning removed for algal bloom at Lake Pegasus

Health warning removed for algal bloom in Ashburton River at SH1

Canterbury DHB’s Community and Public Health unit has lifted its algal bloom health warning issued for the Hakatere/Ashburton River at SH1.

Recent cyanobacteria surveys of the Hakatere/Ashburton River at SH1 have shown the cover of potentially toxic algae (benthic cyanobacteria) in the river has reduced and is now below levels that are of concern to public health.

Warnings remain in place for the Hakatere/Ashburton River at other locations due to ongoing algal blooms. These are:

  • Hakatere/Ashburton River at Boundary Road
  • Hakatere/Ashburton River at Hills Road
  • Hakatere/Ashburton River at the Hāpua (River Mouth)

Facts about cyanobateria:

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • A low cover of the algae can occur naturally but can increase rapidly during warmer months. Algal blooms are influenced by a combination of available nutrients in the water and sediments (such as nitrogen and phosphorus), a sustained period of low and stable flows, and favourable weather conditions (e.g. increased temperature, calm days).
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods.
  • Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the risk of exposure to toxins.
  • If a health warning is in place avoid contact with the water.
  • Although district or city councils may place warning signs, these may not be seen at the numerous river access points, hence the need for people/ dog-walkers to treat every low-flowing river cautiously.

For further information 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 March 2021

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