Toxic algae found in Waimana River

Published: Thu 18 Dec 2008 10:57 AM
HEALTH WARNING: Toxic algae found in Waimana River
Potentially toxic algal mats have been found covering the bed of the Waimana River in the Eastern Bay of Plenty during an inspection by scientists from Environment Bay of Plenty. Areas worst affected include river sections downstream of the Waimana township near Wardlaw and Kirkbride Roads.
People are advised to avoid contact with this section of the Waimana River and be on the lookout for the toxic algal mats elsewhere in the river.
Toxic algae (cyanobacteria) often multiply to excessive levels during periods of warm, dry, sunny weather when rivers levels are low. In rivers they can form extensive black or brownish slime-like mats that cling to rocks and logs. Significant clumps sometimes break off and float free, eventually collecting on vegetation at the water's edge.
“At this stage the Waimana River contains the most extensive mats although other rivers, including the upper Rangitaiki, are showing early signs of mat development” says Toi Te Ora – Public Health Medical Officer of Health, Dr Phil Shoemack.
“The toxic algae that form the mats can release toxins that are potentially harmful to people and animals. Last summer a similar problem occurred in the Rangitaiki River, and on that occasion a dog died following exposure to the algae,” says Dr Shoemack.
Cyanobacteria toxins can trigger asthma and hayfever attacks in susceptible individuals, as well as causing skin rashes, tummy upsets, and even neurological effects such as tingling round the mouth, headaches, general breathing difficulties and visual problems.
“People need to take steps to prevent animals, both farm stock as well as pets, from having direct contact with the mats by keeping the animals away from the affected stretch of river.” Highest risk areas tend to be shallow river margins where infants and dogs are most likely to come in contact with the mats. “Anyone that usually draws their domestic drinking water from lower sections of the Waimana River should also find an alternative source,” he says.
As a similar problem could occur in other rivers at any time, Dr Shoemack advises people to make their own visual assessment of a river and avoid diving in if black and brown algal mats are found covering large areas of the river bed. People should also avoid swimming in or drinking river water that has a strange musty smell.
“If in doubt, go somewhere else,” he says.
Image of the toxic algae (cyanobacteria) mats.
The mats are the dark brown/black patches.
For up to date information on recreational water quality go to
For video clips and images of toxic algae mats follow the link

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