Friday March 24, 2017

​​The Community and Public Health division of the Canterbury District Health Board has lifted its algal bloom health warning issued along the Selwyn River/Waikirikiri at Whitecliffs Domain. This warning was issued on 20th February 2017.

Recent cyanobacteria surveying at Selwyn River/Waikirikiri has shown the cover of potentially toxic blue-green algae (benthic cyanobacteria) in the river has decreased and is now below the levels that are of concern to public health.

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says Environment Canterbury's routine monitoring of rivers and lakes in the Canterbury region has been completed for this summer season.

"It will resume again next summer when there is increased likelihood of cyanobacteria growth," Dr Humphrey says.

"The public is however reminded that there are still some rivers and lakes where warnings remain in place due to algal blooms."

These are:

  • Selwyn/Waikirikiri River at Glentunnel
  • Lake Pegasus
  • Lake Forsyth/Te Roto o Wairewa which also has a Rāhui on the lake
  • Hurunui River at State Highway 7
  • Lake Ellesmere/Te Waihora

These will continue to be monitored and the public advised when the warnings have been lifted.

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.

For further information visit

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



Page last reviewed: 31 March 2017