Algal bloom discovered in Waipara and Ashley rivers.


The potentially toxic algae, Phormidium, has been discovered in the Ashley and Waipara Rivers.

Phormidium – is a thick dark brown or black algae – that attaches to rocks on the river bed. It can be toxic to humans and animals if ingested.

Hurunui District Council Environmental Health Officer, Dianne Morrison, says investigations have shown about 14% of the Waipara River bed near Stringers Bridge is affected and that the mats are now detaching and floating on the surface in shallow waters or settling on the river’s edge. 

The recent hot dry weather could increase the growth of the algal, the detachment of the algal mats and the potential for toxins to be present.

The problem is similar at the Ashley River, with around 30% of the surveyed site on State Highway One revealing algal growth.

Dianne Morrison says anyone camping or visiting the area should avoid contact with the water. Fishermen should wash all fish in CLEAN water.

“Anyone who thinks they have experienced a reaction, should see their GP, and advise they may have been exposed to potentially toxic cyanobacteria.”

The algae exudes a musty smell which is attractive to dogs who are particularly susceptible to poisoning if they eat the brown black mat forming algae. In previous years their have been dog deaths associated with the presence of Phormidium.

Symptoms in animals include lethargy, muscle tremors, fast breathing, twitching, paralysis, convulsions.

Livestock are also at risk and should be provided with alternative drinking water.

Samples from both rivers have now been sent off for analysis to confirm potential toxicity. Results are due next week.

Signs are being posted at key points on the rivers advising of the presence of the bloom and the need to take care.

The warm weather and low flow conditions also create the potential for other rivers to be affected.

For further information contact:                

Dianne Morrison

Environmental Health Officer

Hurunui District Council

P: 03 314 0051