The toxic algal bloom found in Lake Waihola and the Tomahawk Lagoon in the past two days can cause illness in humans and be deadly to dogs, the Otago Regional Council says.
The council is warning the public that they and their animals should avoid contact with the potentially toxic dark blue-green algal bloom in Lake Waihola, south of Dunedin, and the upper Tomahawk lagoon in Dunedin.
Director of environmental information and science John Threlfall said this algae could cause illness in humans and be fatal to dogs.
Otago-Southland medical officer of health Dr Marion Poore said people swimming in water with the bloom had been known to develop allergic reactions such as asthma, eye irritations, rashes, blistering around the mouth, and nose and gastro-intestinal disorders, including abdominal pain, cramps, and diarrhoea.
The higher the concentration of toxins, and the longer the contact with the water, the more severe the symptoms were likely to be so people or animals should not swim in the lake or lagoon and fishermen and boat users should exercise caution, Dr Poore said.
Dogs and livestock were particularly susceptible to algae poisoning because they could consume the algae and should be given alternative drinking water.
Symptoms of poisoning in animals included lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsions. In extreme cases, death could occur in animals within 30 minutes of the initial symptoms.
If illness was suspected from swallowing water with algal bloom people should contact their doctor for medical advice and if an animal became sick, owners should contact their veterinarian immediately, Dr Poore said.
The council would place warning signs about the bloom at the lake and lagoon.