The Otago Regional Council is warning the public,
particularly dog owners, to beware of toxic algal blooms in
rivers and lakes over the summer.
Director of environmental information and science John
Threlfall said yesterday toxic algae could occur in
relatively clean water and he identified phormidium as one of
the most common.
Phormidium forms a thick, brown-black, slimy algae mat on
large rocks, stones, and cobbles. It can detach in mats and
get caught up in river and lake debris.
"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."
Dogs were particularly susceptible.
"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 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 were commonly blue-green in lakes or still
water, but could also be red or yellow. They did not occur
regularly in Otago lakes.
They typically formed thick scums on the surface, and might
also develop foam at the water's edge. They could cause, in
people, allergic reactions such as asthma, eye irritation,
rashes, blistering around the mouth and nose, and
gastrointestinal disorders, including abdominal pain, cramps
Dr Threlfall said reaction depended on the type of toxic
algae, the type of toxins present, and the concentration of
the toxin in the water.
Where humans became ill after swallowing water containing
algal bloom, medical advice should be sought immediately, Dr
Threlfall said, and a veterinarian should be contacted in
cases where animals may have been affected.