Health New Zealand | Te Whatu Ora Pareora River | Pureora State Highway 1 and the Ōpihi River at the Salesyard. These were issued on the 05/12/2024 and the 25/02/2025 respectively.

Recent cyanobacteria surveys of therivers has shown the cover of potentially toxic algae (benthic cyanobacteria) in the rivers have reduced and are now below levels that are of concern to public health.

Dr Cheryl Brunton, Medical Officer of Health for the National Public Health Service, says Environment Canterbury’s monitoring ofboth the Pareora | Pureora and Ōpihi Rivers 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.

For further details visit the Land Air Water Aoteroa website. 

Canterbury region — Land Air Water Aotearoa (external link)

Or contact Te Mana Ora | Community and Public Health on 03 364 1777

Protecting the quality of recreational water — Te Mana Ora (external link)

Public health and mahinga kai gathered from water — Te Mana Ora (external link)