Otago Regional Council and Public Health South are reminding the public to keep their distance from some popular swimming locations in Otago because of potentially toxic algal blooms.
They have reiterated their warning earlier this month for people not to come in contact with the water in these places.
Council environmental information and science director John Threlfall said it has been confirmed that Lake Waihola south of Dunedin, the upper Tomahawk lagoon, and the lower Taieri River near Henley, contained the potentially toxic blue-green algae Anabaena lemmermannii.
However, it could be present in other areas as well.
"This algae, which is dark green, can produce a series of toxins which are then passed to the water and can be fatal to dogs and cause illness in people," he said.
Southern District Health Board medical officer of health Marion Poore said people swimming in water with increased levels of algal 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.
"People should not swim in areas affected by the algae, and other water users, including fishermen and boat users, should exercise caution," Dr Poore said.
Dogs are particularly susceptible to poisoning from both mat-forming and free-floating toxic algae as they enjoy being in the water and can consume these algae.
Livestock are also at risk from poisoning from cytotoxins and should be provided with alternative drinking water.
Symptoms of poisoning in animals exposed to the type of toxins present in anabaena mats include lethargy, muscle tremors, fast breathing, twitching, paralysis, and convulsions. In extreme cases, death can occur within 30 minutes after signs first appear.
The regional council has put out warning signs at the locations where the algae has been found.
Dr Poore said her office has received a number of calls from the public concerned about the safety of eating fish caught in these waters.
"Unfortunately, there is very little information about the potential toxic effects of eating fish caught from waters with a cyanobacteria bloom," she said.
"Before cooking or freezing the fish, the fillets should be rinsed with clean water to remove any contaminants from the cleaning process," she said. "It is also important to wash all equipment in clean water afterwards."