Health warning removed for potentially toxic algal blooms in Canterbury rivers

The Community and Public Health division of the Canterbury District Health Board has lifted its algal bloom health warnings issued for the Selwyn/Waikirikiri River at Glentunnel, the Hurunui River at State Highway 7 and all rivers in the South Canterbury area.

Recent river surveys have shown that the cover of potentially toxic blue-green algae (benthic cyanobacteria) has decreased and is now below the levels that are of concern to public health.

Environment Canterbury's routine monitoring of rivers in the Canterbury region has been completed for this summer season.  It will resume again next summer when there is increased likelihood of cyanobacteria growth.

The public is however reminded that there are still some lakes where warnings remain in place due to algal blooms and monitoring will continue at these sites.

Some warnings remain in place

The warnings remain in place at the following waterways due to ongoing algal blooms;

  • Te Roto o Waihora/Lake Ellesmere
  • Te Roto o Wairewa/Lake Forsyth
  • Lake Pegasus

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.

For further information visit Environment Canterbury's swimming water quality page  or contact Community and Public Health on (03) 364 1777.