High levels of toxic algae found in Kāpiti river

High levels of toxic algae have been found along the Waikanae River in Kāpiti, north of Wellington.

Toxic algae, or cyanobacteria, is harmful to humans and lethal for dogs if ingested.

Red alert level warnings for toxic algae are in place at the old State Highway 1 and Jim Cooke Park.

Greater Wellington spokesperson Penny Fairbrother said that detached algal mats are widespread at both sites, with the potential to harm pets who love playing in the water.

"The warm autumn air and lack of rain has allowed toxic algae to regrow, forming mats at the river's edge that can be very tempting to dogs," she said.

"Toxic algae is a neurotoxin that acts a bit like snake venom. Even the smallest amount - the size of a 50-cent coin - is enough to kill a dog."

She said 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.

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

"You can identify toxic algae by looking out for leathery dark green or black mats clinging to rocks, or clumps of brown at the river's edge. The best antidote for toxic algae is to avoid it all together," Fairbrother said.

Greater Wellington encourages everyone to check the Land, Air, Water Aotearoa website warnings and alerts before visiting rivers in the Wellington Region.