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People and animals, particularly dogs, should avoid the river at Glentunnel until the health warning has been lifted.
There are also other access points along the river that may have cyanobacteria present and people are advised to check for the presence of blue-green algae and avoid contact with it.
Canterbury medical officer of health Cheryl Brunton said the algae looks 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 Brunton 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 is following procedures and monitoring at its 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 Brunton said.
Pets should be taken to a vet immediately if they show signs of illness after coming into contact with algal mats.
People and animals should remain out of the waterways until the warning has 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.
- The algae occurs naturally but can increase rapidly during warmer months.
- It often has a strong musty smell and 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 and people should treat every low-flowing river cautiously.