Health warning removed for algal bloom on two Canterbury rivers

Friday March 23, 2012

‚ÄčThe level of toxic blue-green algae in many Canterbury rivers is decreasing and health warnings are being lifted in some areas.

The Community and Public Health division of the Canterbury District Health Board has lifted its algal bloom health warnings issued for the Ashley River at SH1 and Rangiora/Loburn Bridge and the Hurunui River at SH1.

Recent river bed surveys have shown that the quantity of potentially toxic blue-green algae (benthic cyanobacteria) in these rivers has decreased below levels that are of concern to public health.

Canterbury Medical Officer of Health Dr Cheryl Brunton says Environment Canterbury's sampling of Canterbury's rivers will resume next summer.

However, Dr Brunton says warnings to remain out of waterways because of ongoing algal blooms are still in place at the Waiau River at Waiau township and Te Waihora / Lake Ellesmere

The public will be notified when the above sites have been cleared by Environment Canterbury monitoring.

Facts about cyanobacteria:

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • The algae occur naturally but can increase rapidly during warmer months.
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods with changing environmental conditions.
  • 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.

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Page last reviewed: 24 July 2013