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GWRC warns of toxic algae

Signs on the banks of the Waipoua River in Masterton warning of toxic algae. PHOTOS/FILE

As the countdown until river dips begins, people are asked to start scrubbing up on their knowledge of toxic algae.

Greater Wellington Regional Council wanted to remind swimmers that toxic algae was not only toxic to humans, but was a killer for dogs.

Regional council marine and freshwater team leader Evan Harrison said dogs liked the smell and taste of toxic algae mats.

“Scarier still, an amount as small as a 50-cent piece is enough to kill a dog.

Toxic algae on a rock from the Waipoua River near Colombo Rd last summer

“Vigilance is key as dogs are likely to sniff out the leathery dark green or black toxic algal mats which can wash up at river edges.”

Harrison said prevention was better than any treatment, so checking for warnings online before swimming and letting dogs in the water was paramount.

According to Land Air Water Aotearoa, toxic algae was microscopic organisms that played an important role in many land and aquatic ecosystems.

“In aquatic environments, toxic algal cells can multiply and form blooms in rivers or lakes, known as planktonic, or dense mats on riverbeds, known as benthic.”

Lawa said planktonic blooms were generally found in slow-moving waterways such as lakes, while benthic blooms usually happened in rivers.

“Potentially toxic algae are naturally occurring and live in a range of waterways, from near-pristine to those more impacted by land-use.

“They are an important part of our ecosystem; however, they can become a problem when they increase to high concentrations, forming ‘blooms’.”

Lawa said toxic algae was present most of the year at low levels that did not present much danger.

“Blooms are more common during the summer months, when low rainfall, warm temperatures, the right level of nutrients and more sunlight create an environment where it can thrive.”

Lawa said the natural toxins in the algae, known as cyanotoxins, could be a threat to humans and animals when eaten, even licked, or when water containing the toxins was swallowed.

“Exposure to high levels of toxins from cyanobacteria may result in serious illness or death in humans.

“The effect of cyanotoxins varies from rapid onset of nausea and diarrhoea to, in extreme cases, more serious effects such as liver damage. These toxins have no known antidotes.”

Lawa said children were at more risk than adults for illness from toxic algae because they weighed less and could get a relatively larger dose of toxin.

Regional council senior environment adviser Sheryl Miller said water quality sampling was routinely conducted at over 80 freshwater and coastal sites region-wide and the data shared.

To check for any warnings and alerts for toxic algae, visit lawa.org.nz/explore-data/swimming

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