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Last modified: 19 Mar 2021 1:13pm

Canterbury DHB’s Community and Public Health unit has lifted its algal bloom health warning issued for the Selwyn/Waikirikiri River at Glentunnel. This was issued on 18 November 2020.

Recent cyanobacteria surveys of the Selwyn/Waikirikiri River at Glentunnel has shown the cover of potentially toxic algae (benthic cyanobacteria) at the site has reduced and is now below levels that are of concern to public health.

Canterbury Medical Officer of Health Dr Cheryl Brunton says Environment Canterbury’s monitoring of the Selwyn/Waikirikiri River at Glentunnel has finished for this season and will resume next summer when there is increased likelihood of cyanobacteria growth.

A warning remains in place for ongoing algal blooms for:

  • The Selwyn/Waikirikiri River at Coes Ford
  • Monitoring by Environmental Canterbury will continue until the warning can be lifted for this site.

Facts about cyanobacteria:

  • 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 visit Canterbury Public Health.