Health Warning lifted for Algal Bloom in South Bank Tributary of the Waiau Uwha River above Waiau Bridge

Tuesday 27 May 2025Media release2 minutes to read

Health Warning lifted for Algal Bloom in South Bank Tributary of the Waiau Uwha River above Waiau Bridge

Health New Zealand | Te Whatu Ora has lifted its algal bloom health warning issued for the South Bank Tributary of the Waiau Uwha River above Waiau Bridge. This was issued on 10 February 2025.

Recent cyanobacteria surveys of the Waiau Uwha River above Waiau Bridge have 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 Cheryl Brunton, Medical Officer of Health for the National Public Health Service, says Environment Canterbury’s monitoring of Waiau Uwha River above Waiau Bridge 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: https://www.lawa.org.nz/explore-data/canterbury-region/

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

https://www.cph.co.nz/your-health/recreational-water/

For more information about Mahinga Kai:

https://www.cph.co.nz/wp-content/uploads/saf0112.pdf

ENDS

Media contact: hnzmedia@tewhatuora.govt.nz

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