Deluge flushes toxic algae from local rivers

January 17th, 2013
[from TDC press release]

As well as pleasing domestic gardeners, a positive outcome of the recent deluge of rain has been the flushing of the District's rivers of the toxic blue green algae.

As a result, the risk of dog deaths from consuming toxic algae, or cyanobacteria, will be very low, over the next 2-3 weeks at least, said Tasman District Council resource scientist Trevor James.

"The extended dry period through November and December led to some of the highest coverage of the bed in the Waimea River recorded to date with noticeable occurrences in the Lee and Motueka rivers. However, the rain on 15 January has cleaned it out and it will take another dry period of several weeks before it will build up to concerning levels again.

"If you are a regular user of our rivers and take dogs or toddlers down to play in the water, we strongly recommend that you become familiar with the toxic algae and avoid contact when it is present at a coverage of greater than 20% or the mats are detaching and floating on the water surface.

"The algae that is of most concern is relatively distinctive, forming mats (not filaments) that are soft, dark coloured (black, dark green or dark brown), sometimes thick (over 5mm) and somewhat gelatinous.

"The Council places warning signs at the most popular sites where the risk of contact with the algae growths is known to be greatest."

At present Council is monitoring for this algae at five sites on the Waimea, Lee and Motueka Rivers and is considering expanding this monitoring. Of these sites toxic algae has only exceeded national guidelines for bed coverage on the Waimea River.

"It would be of great assistance if people email the Council or call with sites they think are a problem for the algae so we can review the need for more than the current five sites", said Mr James.

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