29 May 2019
Health warning removed for algal blooms at the Ashley/Rakahuri River at State Highway 1 and the Rangiora-Loburn Bridge
Canterbury District Health Board’s Community and Public Health unit has lifted the algal bloom health warnings issued along the Ashley/ Rakahuri River at State Highway 1 on the 5 February 2019 and at the Rangiora-Loburn Bridge on 15 January 2019.
Recent 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.
Canterbury Medical Officer of Health Dr Ramon Pink says Environment Canterbury’s sampling of Canterbury Rivers has come to an end for this season and will resume next summer when there is increased likelihood of cyanobacteria growth.
• 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.