MEDIA RELEASE
December 3, 2012
ORC warns of possible emergence of toxic algal bloom
The Otago Regional Council (ORC) is warning people to be wary of the possible presence of toxic algae in rivers and
lakes throughout the Otago region this summer.
ORC director of environmental information and science John Threlfall said toxic algae occurs naturally in a wide range
of water quality conditions, including relatively clean waters. It is more likely to be present during the summer months
than at any other time of the year.
In rivers, Phormidium is a common toxic algae which typically forms a thick brown-black slimy algae mat found on large
rocks, stones, and cobbles, Dr Threlfall said
If the mats detach, they may float downstream to become caught up in other debris such as sticks. When the Phormidium
mats die and dry out, they become light brown or white. Either fresh or dried, it can be highly toxic and harmful to
humans and animals.
This is especially true for dogs, as they are particularly susceptible to poisoning from both mat-forming and
free-floating toxic algae.
“Many dogs enjoy being in the water and can eat these algae intentionally or by accident, which can have tragic
results,” Dr Threlfall said.
Symptoms of poisoning in animals exposed to the type of toxins present in Phormidium mats include lethargy, muscle
tremors, fast breathing, twitching, paralysis, and convulsions. In extreme cases, death can occur within 30 minutes
after signs first appear.
Toxic algal blooms are commonly blue-green in lakes or still water, but can also be red or yellow.
They typically form thick scums on the surface, and may also develop foams at the water's edge. In Otago toxic algal
blooms in lakes do not occur regularly.
If an algal bloom is present, people have 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.
Dr Threlfall said any reaction depends on the type of toxic algae, the type of toxins present, and the concentration of
the toxin in the water.
“The higher the concentration of algae toxins and the longer the contact with the water, the more severe the symptoms
are likely to be,” he said.
Where humans become ill or are suspected of being ill after swallowing water containing algal bloom, medical advice
should be sought immediately. Likewise, if animals become sick, a veterinarian should be contacted.