Otago’s dry summer is creating an ideal climate for potentially toxic blue-green algae to flourish in rivers.

This has prompted a precautionary warning from the Otago Regional Council (ORC) for people - dog owners in particular – throughout the region to be on the lookout for the naturally-occurring algae (also known as Phormidium).

The algae has been spotted in many Otago waterways this summer, including the Waianakarua River in North Otago, the Silver Stream near Mosgiel, and in the Manuherikia River in Central Otago.

Warning signs are in place at many popular river locations.

ORC director engineering, hazards, and science Dr Gavin Palmer said where Phormidium is obvious in a river, people should assume that the water is unsafe for their animals to swim in and exercise caution.

In flowing rivers, Phormidium forms thick dark brown or black mats typically found on large rocks, stones, and cobbles.

The mats may separate from the riverbed and float downstream to become caught up in other debris in the river. When the Phormidium mats die and dry out, they become light brown or white.

Dogs are particularly susceptible to poisoning from mat-forming toxic algae as they can consume the algae intentionally or by accident when in the water.

Symptoms of poisoning in animals exposed to the type of toxins present in Phormidium mats include lethargy, muscle tremors, fast breathing, twitching, paralysis, convulsions. In extreme cases, death can occur within 30 minutes after signs first appear.

 
Phormidium in the Lindis River                            Phormidium in the Lower Waianakarua River

For further information contact

Dr Gavin Palmer
Director engineering, hazards, and science
ORC
03 474 0827 or 0274 933960