Elevated levels of toxic algae have been found at Hamilton Burn, a tributary of the Aparima River, near Affleck Road in Northern Southland.

This follows similar alerts earlier this month in both the Waiau River, near Tuatapere, and the Waihopai River.

Warm temperatures and low stable flows are thought to contribute to the annual occurrence of Toxic algae (benthic cyanobacteria) in Southland waterways.

The algae presents as a dark green/brown slime on rocks, or dark brown/black mats at the water’s edge.

Other factors that promote the algae's growth include high levels of nutrients and run-off into waterways.

Environment Southland senior scientist Katie Blakemore said water users and animals should avoid contact with algal mats and remain alert in other parts of the river for algal growth or mats of algae floating in the water.

“These algae can produce toxins that are harmful to people and animals if swallowed, or through contact with skin. People and animals (dogs in particular) should avoid contact with the river and be mindful of the potential health risks, until health warnings are removed.”

Anyone who experiences health symptoms after contact with contaminated water, visit a doctor immediately. If you are concerned that any animals have consumed toxic algae or contaminated water, they should be taken to a vet immediately.

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