Toxic algal bloom in Kahutara River near State Highway 1

Wednesday January 31, 2018

Community and Public Health (a division of the Canterbury District Health Board) has issued a health warning after potentially toxic blue-green algae (benthic cyanobacteria) were found in the Kahutara River near State Highway 1 at Peketa.

"People and animals, particularly dogs, should avoid the water in the Kahutara River near SH1 and the Lagoon until the health warning has been lifted." says Canterbury Medical Officer of Health Dr Alistair Humphrey.

"Although the algal bloom in the Kahutara River is only at a moderate level, the phormidium (benthic cyanobacteria) mats are detaching, floating downstream and accumulating in the Lagoon. So I would advise that the Lagoon is also avoided."

"Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips. Visit your doctor immediately if you experience any of these symptoms. Also let your doctor know if you've had contact with dark brown/black algal mats or water in this area."

Dr Humphrey says that boiling the water from the river does not remove the toxin and therefore should not be consumed.

Animals that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.

People should remain out of the waterways until the warnings have been lifted.

Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.

Facts about cyanobacteria

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • Cyanobacteria 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.

Get further information on swimming water quality in Canterbury (Environment Canterbury). You can also contact Community and Public Health on (03) 364 1777.

Find out more about recreational water issues in your region (Community and Public Health).

Find out safely gathering mahinga kai.

Page last reviewed: 09 February 2018
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