Dogs and people are urged to avoid contact with water in Ruamāhanga River due to a toxic algae flare up.

Red alert level warnings are in place for Ruamāhanga River at Double Bridges and Te Ore Ore due to widespread toxic algae, with detached mats lifting from rocks to accumulate at the river’s edge.

Greater Wellington (Te Pane Matua Taiao) advises people not to swim or let their dogs near the water of Ruamāhanga River from Doubles Bridge to Te Ore Ore.

Greater Wellington senior advisor integration and insights, Penny Fairbrother, says toxic algae is a neurotoxin that acts like snake venom, which can be very harmful to humans and lethal for dogs if ingested.  

“Toxic algae lives on the riverbed, where it’s usually out of reach. But during a flare up like this, thanks to warm weather and a lack of rain, the algae lifts off the rocks and accumulates at the river’s edge, where it poses the biggest risk – especially to dogs who seem to love the smell and will try to eat it if given the chance,” Fairbrother 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 shows signs of lethargy, muscle tremors, fast breathing, paralysis or convulsions, should go to the nearest vet immediately.” 

Above: Toxic algae lifting off rocks at Te Ore Ore.

“Toxic algae grows on rocks in the riverbed and forms leathery, dark green, brown 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.”   

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

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)  

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

Above: Toxic algae at Double Bridges.