Call for action on toxic algae

00:26, Feb 14 2013

The toxic blue-green algae plaguing rivers in Nelson and around New Zealand will get worse, killing more dogs and putting people at risk as well, leading researcher Susie Wood says.

Dr Wood, a Cawthron Institute scientist at the forefront of international research into the naturally occurring cyanobacteria, said at least 50 dogs had died after eating the algae in various parts of New Zealand.

It was also showing up in other countries, and more research funding was urgently needed.

It was surprising that the problem had attracted so little attention, she said, given the lethal nature of the toxin, "one of the most toxic natural compounds you'll ever come in contact with".

Just a couple of grams of the algal mat formed in a bloom were sufficient to paralyse and kill a small dog within five to 15 minutes, she said.

Since 2005, dog deaths have been reported from Southland to Whakatane.


In the Nelson region, the Maitai and Waimea rivers are worst affected. Two dogs have died after eating algae at the Waimea River during the past year and several others have died in recent years after visiting the Maitai.

"When these blooms occur, there are kilograms of toxins in our rivers," Dr Wood said.

While the musty smell of the algal mats was thought to attract dogs, the danger to humans particularly related to small children, who might ingest the algae while playing at the water's edge or swimming, she said.

No cases of human poisoning had so far been reported in the region.

Dr Wood's advice was to take the risk seriously, keep dogs away from rivers after periods of low rainfall, and to always look upstream when swimming to make sure that detached algal mats were not drifting with the current.

Dr Wood said research had shown that increases in the toxic blooms had two causes: changing climate patterns, with longer stable periods of little or no rainfall, and increasing nitrogen levels in rivers as a result of land-use intensification through farming and forestry.

Cyanobacteria was less likely to bloom in more polluted rivers, such as the Waikato, because it needed to be in waterways that were low in phosphorus.

"It really grows in quite pristine, low-nutrient rivers, which have slightly elevated nitrogen concentrations. In some ways, it's an early indicator that our fresh water is degrading."

She said New Zealand had become a world leader in cyanobacteria knowledge largely because of the work of Victoria University PhD student Mark Heath, who had been researching it for five years.

A few hundred thousand dollars in funding would be enough to take the New Zealand response from largely reactive, after dog deaths, to proactive, developing methods to predict when and where the problems would occur, and to help local authorities with their monitoring and warning programmes, Dr Wood said.

"We've got the data now and enough knowledge that, within a year, we could start to take some of those tools to different regions, if we had the funding."

Once a bloom was found in a river, the problem always became worse, she said. When research began after dogs died from eating cyanobacteria from the Hutt River in 2005, the risk was sourced to a single spot.

"Now, 20 to 30 kilometres of that river have huge problems."

As well as the Maitai and Waimea rivers, the Motueka, Lud and Takaka rivers had been found to have increased levels, while the Lee, Aniseed and Roding rivers had not. "We're really seeing a massive increase in it nationally."

This week, Cawthron is hosting two prominent French scientists, Professor Jean-Francois Humbert and Associate Professor Catherine Quiblier, both specialists in planktonic bacteria.

Cyanobacteria is becoming a serious problem in France and this is their second visit, with Dr Wood and Mr Heath also making a study trip to France last year.


Blue-green algae, or cyanobacteria, forms thick, dark-brown mats in the river. Swallowing water containing blue-green algae toxins can lead to vomiting, diarrhoea, abdominal pain, cramps, nausea and other effects in humans. Skin contact can cause irritation of the skin, eyes, nose and mouth.

Exposure to high levels of toxins can result in serious illness or death. If you are concerned about your animals, contact a veterinarian immediately. If you are ill, seek urgent medical attention.

Look for warning signs erected by local authorities.

The Nelson Mail