Warnings signs are now in place at the Rai Falls and the Lions Reserve at the Omaka River due to a proliferation of toxic algae.

Toxic algae are most prolific in shallow river water and are a particular risk to dogs and young children

Continued dry weather is contributing to an increase in toxic algae cover approaching levels that pose a significant risk for dogs and small children. Council is asking people to avoid areas of water where it is present.

The algae form thick brown or black mats on rocks in the riverbed. These mats have a velvety appearance and can become detached from the rocks. They often accumulate along the water’s edge, where they decay releasing a musky odour, which dogs are attracted to.

Council Environmental Scientist Steffi Henkel says the absence of a warning sign in other rivers and streams around Marlborough does not mean that toxic algae are not present. “Council cannot survey all of Marlborough’s extensive stream and river network for toxic algae so it’s impossible to put up warning signs at all affected areas. We rely on the public to be vigilant when walking their dogs along rivers and streams and to keep an eye out for the toxic algae.”

“The toxins in the algae can be dangerous for children and dogs. If your dog ingests toxic algae, you should take it to the vet immediately. Symptoms usually occur within 30 minutes and include panting, lethargy, muscular twitching, paralysis, and convulsion.”

“In humans, contact with toxic algae can cause vomiting, diarrhoea and skin irritation,” Ms Henkel said. “Fortunately, there is still very little toxic algae cover in the Wairau River and we have seen no signs of the algae at the main swimming sites in the Te Hoiere/Pelorus River.”

You can find out more about toxic algae, including how to identify it, on Council’s website: www.marlborough.govt.nz/recreation/swimming-and-boating/toxic-algae

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