NIWA behind spread of didymo to North Island - Anderton

The body responsible for managing New Zealand's freshwater systems was "almost certainly" behind the spread of didymo cells to North Island rivers, Biosecurity Minister Jim Anderton admitted today.

MAF Biosecurity NZ went on high alert late last month when dead cells of the invasive algae, commonly known as rocksnot, were found in water samples taken from the Tongariro, Whakapapa, Mangatepopo and Whanganui rivers as part of Genesis Energy's monthly water quality sampling programme.

Further testing found more dead didymo cells in samples collected at two sites on the Tongariro River.

Mr Anderton today said investigations by Maf Biosecurity and the Crown research institute NIWA had traced the contamination to NIWA's Christchurch facility.

"Contamination of water sampling containers was almost certainly the source of the dead didymo cells found in four central North Island rivers in late October," he said.

Mr Andertson said it had been discovered that NIWA pottle lids sent to Turangi were contaminated with "microscopic amounts of dead didymo cells".

"The lids were held in storage in a laboratory at the NIWA facility in Christchurch, prior to being sent to the North Island for use in sampling," Mr Anderton said.

The Christchurch laboratory was being used to weigh dead samples of the algae at the time.

"It is important to note that at no time could live didymo cells have been transferred from the NIWA facility to the North Island," Mr Anderton said.

He said he had expressed his concern to the chief executive of NIWA, who had assured him there had been a full investigation into the incident and steps taken to ensure it did not reoccur.

Mr Anderton also issued a public apology to the Army, following speculation that it could have in some way involved with the algae's spread.

The public has been urged to wash and dry all fishing gear, boats, kayaks and any other equipment that enters waterways before and after recreation in an effort to stop didymo contamination.


Known also as "rock snot", didymo (didymosphenia geminata) is algae that form dense fibrous mats, with a texture and appearance of dirty brown cotton wool.

They can clog waterways and give rivers a polluted look.

The most likely cause of didymo transfer is through human activity, such as failure to clean and dry boats and fishing equipment.

However, there is a small possibility that animals such as birds could also spread the algae.


- NZ Herald

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