Red alert level warnings are in place for the Waikanae River at Old State Highway 1, where Greater Wellington advises people and dogs to avoid contact with water.
Toxic algae grows on rocks and forms leathery, dark green or black mats. The algae produces oxygen which can lift the algae off the rocks, forming detached mats that accumulate at the river’s edge.
Greater Wellington senior advisor for Integration and Insights, Penny Fairbrother, says it is unusual to see such high levels of toxic algae so early in the season.
“Our summer monitoring season starts in December, so to see this amount of toxic algae in a river at this time of year is concerning,” Fairbrother says.
“We have noticed the Waikanae River has become increasingly problematic for levels of toxic algae, and the warm, still weather we’ve experienced this week has made it spread quickly.”
Toxic algae produces a neurotoxin which is harmful to humans and lethal for dogs if ingested.
“The algae is attached to rocks at the sides and along the bottom of the river, posing the greatest risks to dogs who like diving and fetching,” Fairbrother adds.
“Dogs should be on a leash and kept away from the water. A very small amount of toxic algae – the size of a 50 cent coin – is enough to kill a dog.”
Dogs showing signs of lethargy, excessive panting, tremors or seizures should be taken to the vet immediately.
People who are exposed to toxic algae are advised to call Healthline (0800 611 116) if experiencing symptoms such as nausea, skin irritation, breathing difficulties or numbness around the mouth and/or fingertips.