Health New Zealand | Te Whatu Ora has lifted its algal bloom health warning issued for the entire Ōpihi River Catchment,
which includes the following sites:Ōpihi River at SH79 BridgeŌpihi River at SH1Ōpihi River at Grassy BanksŌpihi River at Saleyards BridgeŌpihi River at Raincliff Bridge.
Recent cyanobacteria surveys of the Opihi River 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.
Dr Ramon Pink, Medical Officer of Health for the National Public Health Service, says Environment Canterbury’s
monitoring of Ōpihi River Catchment will resume next summer when there is increased likelihood of cyanobacteria growth.Facts about cyanobacteria:
· 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.