Toxic algae in Hawea River

Pictured: Phormidium has been sighted in Hawea River, upstream of Camphill Road bridge. | Photo: Wanaka Sun

The toxic algae phormidium has been sighted in Hawea River, upstream of Camphill Road bridge. Phormidium and an increasing number of other cyanobacterial species are known to produce toxins. Known as cyanotoxins, they can be a threat to humans and animals when ingested, licked, or when water containing the toxins is swallowed.

Land, Air, Water Aotearoa (LAWA) explains potentially toxic algae (cyanobacteria or blue-green algae) are microscopic organisms that play a very important role in many land and aquatic ecosystems. In aquatic environments toxic algal cells can multiply and form blooms in rivers or lakes (known as planktonic) or dense mats on river beds (known as benthic). Planktonic blooms are generally found in slow moving water-ways such as lakes while benthic blooms usually occur in rivers. Phormidium is the primary species of benthic cyanobacteria found in Otago.

Exposure to cyanobacteria in humans may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers.

LAWA warns exposure can occur by spending time in or around water where there is a bloom, as your skin is likely to come in contact with the water, or you could ingest the water when doing water-based activities. Children are at higher risk from toxic algae because they weigh less and can get a relatively larger dose of toxin. Even a small amount the size of a 50 cent piece can be enough to cause serious harm if eaten.

Toxins are not removed by boiling, normal filter systems, steri-pen or UV light or by adding household disinfectant.

Anyone experiencing health symptoms after coming in contact with contaminated water should visit their doctor.

Dogs are at the most risk as they like to play and scavenge in the water. Phormidium mats produce a deep earthy odour that dogs seem to be attracted to. Dog deaths have occurred when dogs have eaten phormidium. The risk to dogs is greatest when phormidium mats become detached from the river bed and collect at the river edge where they are easily accessible.

Signs a dog has been poisoned by toxic algae include lethargy, muscle tremors, fast breathing, twitching, paralysis and convulsions. If you suspect that your dog has eaten toxic algae, you should treat it like an emergency and contact your vet immediately. In extreme cases, death can occur within 30 minutes after the first signs of illness appear.

In flowing rivers, phormidium forms thick dark brown or black mats typically found on large rocks, stones and cobbles. Otago Regional Council encourages dog owners to familiarise themselves with phormidium and know what to look for when exercising dogs in or around rivers.

Warning signage is in place at the Camphill Bridge site. It is likely this alert will be in place throughout the summer season.





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