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Health warning lifted for algal bloom in Selwyn River at the Upper Huts

Health New Zealand |Te Whatu Ora has lifted its algal bloom health warning issued for the Selwyn River at the Upper Huts. The health warning was issued on 17 January 2024 and is lifted as of 26 February 2024.

Recent cyanobacteria surveys of the Selwyn River at the Upper Huts 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 National Public Health Service, says Environment Canterbury’s monitoring of Selwyn River at the Upper Huts will continue to the end of this summer and then will resume next summer when there is increased likelihood of cyanobacteria growth.

Facts about cyanobacteria:

1. Appears as dark brown/black mats attached to rocks along the riverbed.

2. 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).

3. It often has a strong musty smell and algal toxin concentrations can vary over short periods.

4. Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the risk of exposure to toxins.

5. If a health warning is in place avoid contact with the water.

6. 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