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Otago Public Reminded About Toxic Algal Blooms


December 21, 2012

Otago Public Reminded About Toxic Algal Blooms

The Otago Regional Council (ORC) 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. The two organisations have reiterated their earlier warning of December 6 for people not to come in contact with the water in these places.

ORC director of environmental information and science John Threlfall said it has been confirmed that Lake Waihola south of Dunedin, the upper Tomahawk lagoon, and the lower Taieri River near Henley, contain 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. The degree of toxicity is impossible to predict, but a test carried out on a sample from Lake Waihola showed that no toxins were present at that time at that point.

Southern District Health Board Medical Officer of Health Dr Marion Poore said people swimming in water with increased levels of algal bloom have been known to develop allergic reactions: 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.

Any reaction depends on the type of toxins present, and the concentration of the toxin in the water. The higher the concentration of toxins and the longer the contact with the water, the more severe the symptoms are likely to be. It is difficult to know whether toxins are present at any one time or location, therefore a precautionary approach is strongly recommended.

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 intentionally or by accident. 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, convulsions. In extreme cases, death can occur within 30 minutes after signs first appear.

“In the case of illness or suspected illness after swallowing water containing algal bloom, seek advice from your doctor. If your animals become sick, contact your veterinarian immediately," Dr Poore said.

ORC has put out warning signs at the locations where the algae has been found, but not all sites will be known.

Dr Poore says 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.

Some algae toxins have been found to accumulate in fish tissues, especially in the internal organs such as the liver and kidneys. Toxin accumulation studies suggest that the muscle (fillet) tissue is less affected by algae toxins.

Dr Poore said people choosing to eat fish caught from waters affected by a blue-green algae bloom should use gloves when removing the fat, skin, and organs before cooking, and be careful not to cut into the organs.

Before cooking or freezing the fish, the fillets should be rinsed with clean water to remove any contaminants from the cleaning process.

It is also important to wash all equipment in clean water afterwards.

“As a precaution, we advise against eating any freshwater shellfish such as kakahi or freshwater mussels,” Dr Poore said.

“For those people who eat a lot of fish taken from cyanobacteria bloom-affected waters there is a potential risk of accumulation of toxins in their system. Limiting the number of fish meals to two per week will help avoid this situation,” she said.


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