Canterbury DHB’s Community and Public Health unit has lifted its algal bloom health warning issued for the Waimakariri
River at Thompsons Road. This was issued on 1 December 2020.
Recent cyanobacteria surveys of the Waimakariri River at Thompsons Road has shown the cover of potentially toxic algae
(benthic cyanobacteria) in the river has reduced and is now below levels that are of concern to public health.
Canterbury Medical Officer of Health Dr Ramon Pink says Environment Canterbury’s monitoring of the Waimakariri River at
Thompsons Road will continue to the end of this summer.
“Monitoring will then resume next summer when there is increased likelihood of cyanobacteria growth,” says Dr Pink.Facts about cyanobateria:Appears as dark brown/black mats attached to rocks along the riverbed.A low cover of the algae can occur naturally but can increase rapidly during warmer months. Algal blooms are influenced
by a combination of available nutrients in the water and sediments (such as nitrogen and phosphorus), a sustained period
of low and stable flows, and favourable weather conditions (e.g. increased temperature, calm days).It often has a strong musty smell and algal toxin concentrations can vary over short periods.Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the
risk of exposure to toxins.If a health warning is in place avoid contact with the water.Although district or city councils may place warning signs, these may not be seen at the numerous river access points,
hence the need for people/ dog-walkers to treat every low-flowing river cautiously.
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