Red alerts are in place for Hutt River at Silverstream, Waipoua River at Colombo Road, and Ruamahanga River at Double Bridges and Te Ore Ore.
Greater Wellington Regional Council advised people not to swim or let their dogs near the water.
The algae is a neurotoxin that acts like snake venom and is extremely harmful to humans and lethal for dogs if ingested.
“Toxic algae lives on the riverbed, where it’s usually out of reach,” Greater Wellington senior advisor integration and insights, Penny Fairbrother said.
“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.
“Even a small amount of toxic algae, the size of a 50-cent piece, can be enough to kill a dog.”
People should check the LAWA website for toxic algae warnings and alerts before visiting rivers in the Wellington region.
People who were feeling unwell after being in contact with algae were asked to see a doctor or contact Healthline on 0800 611 116.
Anyone who suspected their dog had swallowed toxic algae should visit the nearest vet immediately.
Greater Wellington was monitoring popular swimming spots weekly. It asked people to check the LAWA website for warnings and alerts before visiting rivers in the Wellington region.
Originally published on rnz.co.nz, written by Madleine CarrWhite, Massey Journalism Student
