A potentially toxic blue-green algae has returned to Lake Waihola.
The Otago Regional Council yesterday issued another warning for the public to keep their dogs away and avoid contact with the lake.
Council environmental information and science director John Threlfall said the lake had been given the all clear earlier in the month but the algae had come back.
The dark green algae could produce toxins which were passed into the water and could be fatal to dogs and make people ill.
It was discovered in Lake Waihola and Tomahawk Beach in early December.
Otago medical officer of health Dr Marion Poore said people should not swim in the lake and fishermen and boat users should exercise caution.
Signs would be put up where the algae had been found and the council would continue to monitor the situation.
