Water quality monitoring by Hawke’s Bay Regional Council staff indicates that potentially toxic algae levels are present on the Tukituki River, at Black Bridge near Haumoana.
Parts of the Tukituki River are prone to algal growth in summer, due to lower water flows, higher water temperatures and nutrients in the water. Green strand algae is harmless but black Phormidium bacteria growth on the rocks is potentially toxic for humans and dogs. It can detach from the rocks and dry as mats on the sides of the rivers, and these can also be toxic.
“Our advice is to always treat the black growth on rocks in the water and the drying mats as toxic, stay out of the water if you see it, and swim or walk your dog elsewhere,” says HBRC’s Senior Environmental Scientist Anna Madarasz-Smith.
She adds that science has not yet identified when Phormidium turns toxic or why, so to be safe it should always be treated as harmful.
Warning signs would be put up at affected areas by HB District Health Board staff, but people were urged to avoid contact with the cyanobacteria mats and to keep animals away.
What are Cyanobacteria?
Cyanobacteria are single celled creatures that live in water environments. Cyanobacteria have characteristics in common with both bacteria and algae. In warm nutrient rich conditions free-floating cyanobacteria cells can multiply quickly to form what are known as algal blooms. Large numbers of Cyanobacteria can also grow as mats on river and lake beds and these mats can sometimes detach and float to the surface. Some cyanobacteria species produce toxins (cyanotoxins), which pose a risk to humans and animals when consumed in drinking water or by direct contact during recreational activities.
29 March 2018
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