The Waihopai River. Photo: Supplied / Cawthron Institute
Environment Southland said it was found during monitoring observations and an alert is in place.
Toxic algae can naturally occur during fine conditions and stable river flows. It is identified as dark brown or green slime on rocks or dark brown/black mats at the water's edge.
People are being urged to avoid contact with it and keep dogs and children away from affected areas.
The algae can pose significant health risks to people and animals if swallowed or through contact with skin.
The alert for the Waihopai River at Kennington has been removed, however there is still a toxic algae alert for the Waiau River near the Excelsior Creek inflow.
