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Traces of an invasive pest have been found in central North Island rivers - a discovery that could mean economic calamity for the region's world-famous trout fishing.
Biosecurity NZ said yesterday that samples of water from the Whanganui, Tongariro, Whakapapa and Mangatepopo Rivers contained dead didymo cells.
Didymo poses no health risks to humans but can grow rapidly and choke rivers, destroying food that sustains fish.
Until now it was thought to be confined to South Island rivers.
Fish and Game chief executive Bryce Johnson said he expected more tests would show live didymo cells in the North Island. "I'd be most surprised if it's not there."
The discovery of dead cells meant live cells had been present, he said.
"It's a real worry - the last thing we want to get to the North Island. We'd hoped to get a good strong boundary from the South Island."
Didymo was discovered in the Lower Waiau River in Southland in October 2004.
Mr Johnson said it made rivers look terrible, leaving them coated in brown slime.
"It has an aesthetic impact and is a big nuisance for anglers. It's like having dirty toilet paper floating in the water ... It looks revolting."
Brett Cameron, of Central Plateau Fishing in Taupo, was shocked to hear last night of the discovery.
"That's the worst news you could get. The Tongariro is a world-famous spawning river for rainbow trout. If didymo is here it'll shut Taupo fishing."
Mr Cameron said it would have a devastating effect: "My business is taking people fly fishing ... This would shut me down."
Tackle shops and a "fair chunk of Taupo's economy" would be affected.
Mr Cameron said the Whanganui River was an "absolutely pristine waterway" up in the headwaters and the Mangatepopo was a "beautiful little stream".
Trout fishing tutor Harvey Clark said it would be an absolute disaster if didymo was found in the Tongariro River, where the World Fly Fishing Championships are to be held next year.
Taupo fishing guide Brendon Mathews said many anglers were critical of measures taken by Biosecurity to stop didymo from spreading to the North Island.
"Everyone has been waiting to hear it [has been discovered here] but I feel like someone has walked over my grave. If it spreads this could be a major disaster for fishing tourism. You'll have people leaving the district. It's a tough enough industry as it is."
Mr Mathews said there were also problems with it getting into power plants in the area and blocking the intakes.
Advocates for the Tongariro River president Heather Macdonald's immediate reaction was "thank God it's dead didymo".
She said some river users had held the view the volcanic makeup of the waterways might mean didymo was unable to live in the area.
"All I can hope is that our waters have proved toxic to didymo."
The dead cells were in samples taken as part of Genesis Energy's monthly water quality sampling programme.
Biosecurity NZ executive David Hayes said the agency was taking the discovery seriously and was treating it as a matter of urgency.
He said live cells needed to be present before a waterway could be confirmed as infected with didymo.
All sites where dead cells were found would be retested and work had begun on testing sites nearby.
Mr Hayes said that no decision had been made to close the rivers but people should avoid using them.
MAF Biosecurity is working with the Department of Conservation, Fish and Game, Genesis Energy, Tuwharetoa Maori Trust Board, and the New Zealand Recreational Canoeing Association.
Staff will be at popular spots reminding river users to decontaminate equipment.
All items should be cleaned for at least one minute with a 5 per cent solution of dishwashing liquid or nappy cleaner, dried to the touch and left for another 48 hours before use in another waterway.
The application method is important, as water absorbent materials such as felt-soled waders and boots require longer soaking times to allow thorough saturation.
Felt-soled waders require soaking for at least 40 minutes in hot water kept above 45degC or soaking for 30 minutes in hot water kept above 45degC containing 5 per cent dishwashing detergent or nappy cleaner. Anglers may wish to use rubber-soled footwear instead, which are easier to clean and dry.
If cleaning an item was not practical, it should be allowed to dry. Once touch dry, it should be left dry for another 48 hours. Freezing any item until solid will also kill didymo. If cleaning or drying is not practical, restrict equipment to a single waterway.
"This is something all people should be doing regardless of location or perceived risk," Mr Hayes said.
- Additional reporting NZPA
