Media release

Public reminder to look out for potentially toxic algae this summer

Thursday 21 December 2017

High levels of naturally occurring Phormidium or blue green-algae have been reported at the Confluence of Dunstan Creek and Manuherikia River today. Existing alerts are in place at Cardrona River.

The recent warm weather which has resulted in low river flows could mean the increased presence of naturally occurring Phormidium or blue-green algae in the region’s waterways over summer. High levels of Phormidium have been confirmed at the confluence of Dunstan Creek and Manuherikia River today, which has prompted a warning from Otago Region Council (ORC) to avoid contact with the waters. In addition, there are existing toxic algae alerts in place in the Cardrona River.

With more sunshine predicted and plenty of opportunities for holidaymakers to take to the water this summer, ORC would like to remind people recreating in or around Otago’s lakes and rivers to be mindful of algal blooms that may be present.

Manager Resource Science Dr Dean Olsen said “the downside to this pleasant weather we’ve been having lately is that it does create the perfect conditions for Phormidium to be present in some of the region’s waterways, including those with good water quality.”

“Phormidium can produce natural toxins, which can be a risk to human and animal health if they come into contact with it,” he said.

“At a certain point of the algae’s life-cycle the dark brown/black mats can detach from rocks and wash up at the water’s edge, which can be particularly risky for dogs,” said Dr Olsen. “I encourage dog owners to take the necessary steps to protect their dogs. It’s important that dog owners familiarise themselves with what toxic algae looks like and ensure that their dog doesn’t eat anything in the water or from the water’s edge.”

Pets should be taken to a vet immediately if they show signs of illness after coming into contact with algal mats. The most common signs that a dog might have consumed toxic algal material are lethargy, muscle tremors, fast breathing, salivation, twitching, paralysis and uncontrolled shaking, convulsions, or frothing at the mouth soon after being in the water. There have been cases in New Zealand of dog deaths associated with toxic algae. Anyone concerned their pet may have consumed toxic algae should contact their vet immediately.

In humans, exposure to Phormidium may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers. Anyone experiencing health symptoms after contact with contaminated water should contact their doctor.

“If you’re thinking of going for a swim, I’d recommend checking the ‘Can I Swim Here’ website first. If you happen to come across any blue-green algae, avoid swimming in the area, and please call our pollution hotline on 0800 800 033 or complete an online incident form on the ‘Can I Swim Here’ website.” Said Dr Olsen.


 ‘Can I swim here?’ website -

For more information and a video for what toxic algae looks like –

A mat of Phormidium coating the bed of a North Otago river

For more information contact:

Dr Dean Olsen  
Manager Resource Science
Ph 0800 474 082

Communications contact

Sian Sutton
Director Stakeholder Engagement

Ph 0800 474082 or 027 575 1799