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Global warming and land use are increasing toxic algae and the dangers it poses to those using waterways, a freshwater scientist says.
Every summer dozens of local councils warn their residents about toxic algae creeping into waterways. Dog owners are warned to keep their pets away so they don't eat the algae and get sick.
Canterbury rivers with warnings in place include the Waikirikiri/Selwyn River, from Whitecliffs Domain down past Glentunnel Camping Ground, and the Whakatipu/Twizel river at the picnic area upstream of State Highway 8.
Environment Canterbury monitors more than 100 popular recreational sites and issues health warnings when an increased risk of cyanobacteria or faecal contamination is present.
Cawthron Institute senior freshwater scientist Susie Wood told Summer Times the public should contact their regional council to flag any concerns they have about their favourite swimming holes this summer.
Wood is a senior scientist whose expertise in biosecurity, marine and freshwater and algal biotechnology is used across Cawthron.
Her passion stems from experiences growing up with typical Kiwi camping trips by lakes and rivers, which led to university studies in biology, ecology and conservation.
She chose to study cyanobacterial algal blooms for her PhD, after discovering a lack of knowledge about the species in New Zealand. She is now considered one of the world experts in cyanobacteria.
"With regards to the toxic algae we know that this is a high-risk time of year," she says.
"The temperatures over the last month or so have been extremely warm and this is the type of conditions where the toxic algae really thrives.
"So we’re seeing generally in the last decade we’ve seen an increase in the amount of algae in both our rivers and also in the lakes across the country."
Wood said there are two types of algae dangers we need to be aware of.
"In our rivers it’s what we call benthic algae, or toxic algae and it grows on the rocks on the bottom of the rivers and it forms very thick brown mats.
"At certain times when the river flow is low, the mats will also detach and they will float and accumulate along the edges of the river and that’s when they’re really available to things like dogs, or perhaps even children playing at the edges of rivers.
"They produce a rather potent toxin. I’d say in the last decade we’ve had probably over 200 dog deaths across the country where these dogs have been attracted to the rotting odour and or smell of these mats and they go to consume them."
She said councils do a great job monitoring rivers and swimming holes, but their staff can’t be everywhere. She is encouraging the public to get on to their regional council to look into any areas of concern and in places where they swim.
People often get into trouble in lakes, Wood says.
"In lakes the toxic algae grows in the water and it’s floating. It forms what we call blooms, which can also accumulate at the edge of a lake and form what we call a scum.
"Usually they’re bright green and again it forms at the places where we tend to be swimming or recreating and they also produce toxins that create health risks."
Risks include accidentally ingesting it while swimming, which can be easily done if there’s small amounts in the water.
"It’s unlikely that you would ingest a lethal amount. It can make you sick. Common symptoms would be Gastroenteritis and fevers.
"But I guess the big concern in this would be if you eat a good chunk of it, a small toddler might put a chunk it their mouth accidentally, that’s probably the highest risk in terms of potential death or serious illness."
You don’t need to worry about all algae, though, particularly the slippery stuff at the bottom of lakes that you may need to navigate to have a swim. There are natural types of algae that serve a beneficial propose in waterways.
The one to concern yourself with is a very dark black/brown coloured algae, which can have a musky smell, she says.
But if your dog ingests some of the toxic algae, she says time is of the essence to get it to the vet a fast as possible.
"Get your animals to the vets. They are very fast-acting toxins, the ones in the rivers in particular. So, the faster you can do so the better."
The same applies for humans – get to a doctor as soon as possible.
The problem is growing due to multiple causes, she says.
"One absolutely is our climate is changing. We’re having these warming summers… and we’ve got longer periods without rainfall which allows them to grow much more extensively in rivers.
"And, of course, it is also due to what we’re doing in the land along the water…it’s symptomatic of the changes of our water quality."
She says stopping nutrients and sediments entering the rivers is an absolute must.
"Things like planting native vegetation along the edges of our rivers and streams. Any of those kind of actions, which we’ve heard a lot about in recent years, to help water quality."