A toxic algae red alert is in place on the Waipoua River where it passes under Colombo Road in Masterton.

Greater Wellington is urging people not to swim in this part of the river, or let their dogs enter the water. Dog walkers should also avoid the riverbank as detached algal mats have been found at the river’s edge.

The regional council’s manager of knowledge and insights, Evan Harrison, says toxic algae contains a neurotoxin that acts like snake venom, which can be harmful to humans and lethal for dogs if ingested.

“We strongly advise people to avoid contact with the water, and to keep dogs and children away from the river’s edge,” Dr Harrison says.

“Even a small amount of toxic algae, the size of a 50-cent piece, can be enough to kill a dog.”

Dog owners who think their animals have swallowed toxic algae, or that show signs of lethargy, muscle tremors, fast breathing, paralysis or convulsions, should go to the nearest vet immediately.

People who have been in contact with toxic algae and are feeling unwell, should see a doctor or ring Healthline on 0800 611 116.

Greater Wellington is currently monitoring popular river swimming spots for toxic algae on a weekly basis.

The community is advised to check the LAWA website for toxic algae warnings and alerts before visiting rivers in the Wellington region this summer.

“Toxic algae blooms form naturally when river temperatures rise,” Dr Harrison says.

“It’s important everyone knows how to spot toxic algae to keep their pets and whānau safe.”

Toxic algae 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, and have a musty smell that attracts dogs.

To learn more about toxic algae, visit: Greater Wellington — Toxic algae (gw.govt.nz)

To check for toxic algae alerts in the Wellington region, visit: Land, Air, Water Aotearoa (LAWA) -

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