Toxic algae on a rock at a river's edge. Photo: Supplied / Greater Wellington Regional Council
Greater Wellington warns that people and dogs must avoid contact with water in the Wairarapa due to toxic algae.
Red alert level warnings are in place at Ruamāhanga River from Doubles Bridge to Kokotau.
There are moderate amounts of toxic algae mats on the river's edge.
Dr Evan Harrison from Greater Wellington said the toxic algae was a neurotoxin that acted like snake venom.
It could be very harmful to humans and lethal for dogs if ingested, he said.
"We're advising that people avoid using the stretch of Ruamāhanga River from Doubles Bridge to Kokotau, but if you do go there keep dogs and small children away from the river's edge," Harrison said.
"Even a small amount of toxic algae, the size of a 50-cent piece, can be enough to kill a dog."
Owners who think their dogs have swallowed toxic algae - or shows signs of lethargy, muscle tremors, fast breathing, paralysis or convulsions - should go to the nearest vet immediately.
People who have been in contact with it and are feeling unwell should see a doctor or ring Healthline.
Harrison advised checking the Land, Air, Water Aotearoa website for toxic algae warnings and alerts before visiting rivers in the Wellington region.
"Toxic algal blooms form naturally when temperatures increase, and calm weather conditions provide a stable growing environment.
"[It] grows on rocks in the riverbed and forms leathery, dark green or black mats, which can break off and accumulate at the river's edge.
"As the algal mats dry out, they can become light brown colour and have a distinctive deep earthy or musty smell.
"It's important everyone knows how to spot toxic algae to keep their pets and whānau safe."
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