Health Warning for Ashley River Bridges Ends

Published: 14-May-2019

Please Note: This article was first published in January 2018 and no longer contains current information.

The algal bloom health warning that was issued along the Ashley/ Rakahuri River at State Highway 1 and at the Rangiora-Loburn Bridge has been lifted.

20180124_SwimmingKidsRiver monitoring by Environment Canterbury, which included cyanobacteria surveying of the water in the Ashley/Rakahuri River, has shown the coverage of potentially toxic blue-green algae (benthic cyanobacteria) in the river has decreased and are now below the levels that are of concern to public health.

This has resulted in the warnings around the two bridges, which were put in place either side of Christmas, no longer being required.

Canterbury Medical Officer of Health Dr Alistair Humphrey says Environment Canterbury’s sampling of the Ashley/Rakahuri River, alongside other water flows within the Waimakariri District, will continue to the end of this summer and then will resume next summer when there is increased likelihood of cyanobacteria growth.

The algae occur naturally but can increase rapidly during warmer months – river users are advised to treat every low-flowing river cautiously.

Both areas of the river that were covered by the warning are popular with families for riverside walks, with the previous risk extending to pets, as the members of the community regularly exercise their dogs near both bridges.

Facts about cyanobacteria:

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • The algae occur naturally but can increase rapidly during warmer months.
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods with changing environmental conditions.
  • 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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