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Health warning removed for algal blooms on the Selwyn River

March 31, 2014

Health warning removed for algal blooms at Glentunnel and Whitecliffs on the Selwyn River

The Community and Public Health division of the Canterbury District Health Board has lifted its algal bloom health warnings issued at Whitecliffs and Glentunnel on the Selwyn River / Rakahuri, issued on January 20, 2014 and February 14, 2014 respectively.

Recent surveys at Whitecliffs and Glentunnel on the Selwyn River / Rakahuri have shown the quantity of potentially toxic blue-green algae (benthic cyanobacteria) in the river has decreased and concentrations are now below the levels that are of concern to public health.

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says Environment Canterbury’s sampling for the summer season has now stopped and therefore the public will need to be aware of the potential for algal blooms themselves.

“The growth of blooms is however unlikely because of the cooler weather and the seasonal nature of the blooms,” Dr Humphrey says.

“Environmental Canterbury will resume sampling again next summer when there is an increased likelihood of cyanobacterial growth.”

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.
• Exposure to an algal bloom can cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips. If you experience any of these symptoms visit your doctor immediately and please let your doctor know if you have had contact with lake water when there is a health warning in place.

For further information visit

Or contact Community and Public Health on (03) 364 1777.


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