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Two more health warnings after potentially-toxic cyanobacteria discovered

potentially-toxic cyanobacteria

Canterbury District Health Board’s Community and Public Health unit has issued two more health warnings after potentially-toxic algae (benthic cyanobacteria) was found in Selwyn/Waikirikiri River downstream of the Glentunnel Swimming hole and Waipara River at Teviotdale.

People and animals, particularly dogs, should avoid these areas until the health warning has been lifted.

Canterbury Medical Officer of Health Dr Alistair Humphrey says the algae look like dark brown to black mats and can produce toxins harmful to people and animals.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips,” Dr Humphrey said.

“If you experience any of these symptoms, visit your doctor immediately, also let your doctor know if you’ve had contact with dark brown/black algal mats or water in this area.”

The Selwyn District Council are following agreed procedures and monitoring their nearby drinking water intakes.

“No-one should drink the water from the river at any time, even after boiling the water from the river, it does not remove the toxin therefore should not be consumed,” Dr Humphrey said.

Pets should be taken to a vet immediately if they are showing signs of illness after coming into contact with algal mats.

People and animals 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 via the Health Warnings page, LAWA and on Facebook at Canterbury Water.

Note: The Waipara River at Teviotdale site is not included in the Can I Swim Here? weekly E.coli monitoring programme. However, we do monitor a number of additional sites, including this one, for cyanobacteria cover due to them being popular for paddling and walking dogs.

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.

Source: Environment Canterbury

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