New Zealand is in the heart of its summer season with record-breaking temperatures in many regions. Not surprisingly, dogs will want to go swimming to cool off.

Each summer, we have warnings about toxic Algae and how it can kill your dog.  I first wrote about this subject over 10 years ago, in 2013, for NZ Dog World magazine. This post updates the original.

There’s a deadly toxin lurking in many of New Zealand’s rivers and lakes.  The savvy dog owner needs to understand it so you can protect your dog.

That toxin is produced naturally by blue-green algae, or cyanobacteria.  ‘Blue-green algae have existed on earth for millions of years,’ says Mark Heath, a researcher whose PhD thesis focused on why algal blooms form in rivers.  ‘However, it is human-induced changes to the environment that have created the ideal situations for the algae to flourish’.

‘We know that the algae have optimal growing conditions during the summer months, when there has been a stable period of little to no rainfall and warm conditions,’ says Susie Wood, Heath’s supervisor and a researcher at the Cawthron Institute.  ‘Nutrients, which are often increased in waterways by land–use intensification, act as the algae’s food source and climate change means longer periods of little rainfall and warm temperatures.’

The algal mats float to the surface and collect on the margins of rivers and in stagnant pools of water.  Dogs are attracted to the earthy smell of the algae and they will readily lick or eat it.  The algae exude a powerful neurotoxin and only a small amount is enough to cause a dog to become ill and die.

Symptoms may include panting, twitching, convulsions, muscle tremors and lethargy.  There is no antidote to the poison and so if you suspect your dog has ingested the toxin, you need to rush to the nearest vet to have its stomach pumped and have activated charcoal administered.  Since the toxin is very fast-acting (some dogs die within 30 minutes of ingestion), prevention is the better course of action.

Dog owners need to be able to ‘spot’ the algae, which often is a dark green/brown to black colour as seen in the photo.  These mats have a velvety texture and a musky smell. If there has been a period of about two weeks without rainfall (which induces ‘flushing flows’ in rivers), then you should assume that conditions are ideal for the algae.  Walking a dog on lead is advised so you can keep a close watch on what your dog takes an interest in. ”If in doubt, keep them out.”

Vets should report a dog death to the regional council but reporting is not mandatory, meaning that many cases are likely to go unreported.

Rivers known for algal blooms include the Hutt River (Wellington region), the Selwyn and Ashley rivers (Canterbury region) and the Tukituki River (Hawke’s Bay).  The algae can also form in lakes which act as a sink for nutrient-enriched waters. In lakes, ponds, and lagoons, the algae is likely to be present if the water is cloudy or discoloured or has scums or small globules suspended in the water.

Dog owners should familiarise themselves with their regional council’s website for algal blooms in their area.

Kathleen Crisley, Fear-Free certified professional and specialist in dog massage, rehabilitation and canine fitness,  The Balanced Dog, Christchurch, New Zealand