Greater Wellington Regional Council [GWRC] is urging people to avoid the Waipoua River where it passes under Colombo Rd, due to elevated levels of toxic algae.
The alert level has been increased to red after being bumped to orange less than a month ago.
Red is the highest alert level and means the river has been assessed as a high health risk and is unsuitable for swimming.
A spokesperson for GWRC said this alert level is normal for December and all summer months, while noting that “heavy rain can sometimes wash away toxic algae, so warning levels may change”.
GWRC manager of knowledge and insights Evan Harrison said toxic algae contains a neurotoxin that acts like snake venom and 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,” Harrison said.
Popular river swimming spots are monitored by GWRC on a weekly basis for toxic algae, and Harrison emphasised the importance of public awareness.
“Toxic algae blooms form naturally when river temperatures rise,” Harrison said.
“It’s important everyone knows how to spot toxic algae to keep their pets and whānau safe.”
Toxic algae grow on rocks in the riverbed and form leathery dark green or black mats. which can break off and accumulate at the river’s edge.
Dog walkers are urged to avoid the riverbank as algal mats have been found there.
As the algal mats dry out, they can become light brown and have a musty smell that attracts dogs.
A piece of toxic algae the size of a 50-cent coin can be enough to kill a dog.
Dog owners who think their animals have swallowed toxic algae, or whose pets 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.
It is advised to check the Land Air Water Aotearoa website for toxic algae warnings and alerts before visiting rivers in the region this summer.
