28 January 2019

Monitoring has identified moderate cover of potentially toxic cyanobacteria algae in the Waihao River near Bradshaws Road. Community and Public Health have therefore issued a health warning and signage will be erected at that site. Once monitoring indicates that these rivers are safe, the signs will be removed. There are also other access points along the Waihao River that may have cyanobacteria present and people are advised to check for the presence of cyanobacteria and avoid contact.

Humans 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 algal mats can produce toxins harmful to humans and animals.

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

“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.”

“No one should drink the water from the river at any time”, as boiling the water from the river does not remove the toxin.

Animals should be taken to a vet immediately if they come into contact with the contaminated rivers.

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

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.

Further information on cyanobacteria is available from ECAN: https://www.ecan.govt.nz/your-region/your-environment/water/cyanobacteria-warnings/ For more information on health effects, contact Community and Public Health on (03) 687 2600.

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