Didymo hits the Waimakariri

Biosecurity measures have been tightened for this weekend's Coast to Coast event after didymo was found in the Waimakariri River for the first time.

North Island competitors will have their kayaks washed and stickered when they leave the Waimakariri so they can be cleared by biosecurity officials at the Picton ferry terminal when they return home.

MAF Biosecurity New Zealand officials will also be present at a jet boat expo on the river over the weekend.

The government agency said yesterday that the invasive algae had spread to the Waimakariri River, but it was unlikely it would grow in the river in large quantities.

The pest, also known as rock snot, has spread to more than 100 rivers and creeks in the South Island but has not yet been detected in the North Island.

The agency's South Island operations manager, Jeff Donaldson, said the scouring action of sediment would prevent major didymo growth in the Waimakariri.

"There are only didymo cells in the river at the moment. The Waimakariri has so much sediment movement that you probably will not see the big biomass material that happens in other rivers," he said.

"The sand and grit will keep the rocks clean. It tends to clean itself."

Donaldson said it was a shame didymo had spread to the Waimakariri after an awareness campaign to clean and dry any equipment when changing rivers.

"It is disappointing that it has got there now because we have watched that river so well and thought the campaign had worked and people were being responsible. It only takes one person to ignore it," he said.

"There is so much recreational activity on that river. It is a very big river and so many people use it, but it would definitely be human intervention."

Donaldson said any future irrigation schemes using the river's water would have to take great care to prevent didymo growth blocking pipes.

Didymo has been detected downriver from Woodend.

Gregg Peacock, a jet boat driver for Waimakariri business Alpine Jet, said he hoped it would not spread upriver.

"No-one is going to be happy about it. Our boats are always in the same river, but we are very careful about boats that have been in other rivers," he said.

"It is not a pretty thing, but hopefully the nature of the Waimak will mean it won't grow."

- © Fairfax NZ News