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A potentially toxic algae which appeared in Otago waterways last month is disappearing, but has been replaced by another potentially lethal algae.
The Otago Regional Council warned the public last month to avoid Lake Waihola, Tomahawk lagoon and the Taieri River at Henley because of the presence of the toxic blue-green algae, which can produce toxins capable of
causing illness and irritation of the skin, eyes, nose and mouth.
Water samples at the locations this week confirmed that the algae had dissipated, ORC resource science manager Matt Hickey said yesterday. However, people using the three locations now needed to be alert to the possible presence of another potentially toxic algae called Phormidium.
''Unlike the blue green algae which has caused problems in Lake Waihola and Tomahawk lagoon, Phormidium is found in rivers and streams and typically forms a thick brown-black, slimy algae mat found on large rocks, stones and cobbles,'' Mr Hickey 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, the algae can be highly toxic and potentially harm animals and people.''
Dogs were particularly susceptible to poisoning from the algae, with symptoms including lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsions.
In extreme cases of animal poisoning, death could occur within 30 minutes of symptoms appearing.
If people became ill, or suspected they had swallowed water containing algal bloom, medical advice should be sought immediately, Mr Hickey said.