Sustained attack on lake weed

Divers will take to Lake Wakatipu tomorrow in a bid to keep it clear of lake weed. Photo: ODT
Divers will take to Lake Wakatipu tomorrow in a bid to keep it clear of lake weed. Photo: ODT
Divers will work by hand and with underwater chainsaws in Lake Wakatipu tomorrow  fighting to keep lagarosiphon out of the water, in an operation that has not been attempted before.

Land Information New Zealand (LINZ) biosecurity manager Dave Mole said the task was highly technical and challenging.

"Given it hasn’t been attempted before it may need to be stopped due to its complexity and risk.

"But, all going to plan, subject to safety considerations and river conditions, we’re confident the work can be completed within approximately two to three weeks."

The work was expected to cost about $142,000. It was funded by the Otago Regional Council with support from Linz, the Queenstown Lakes District Council and other members of the Lake Wakatipu Aquatic Weed Management Group.

The divers, who would also work with barges and other equipment, were scheduled to begin removing dead, submerged willow trees from the Upper Kawarau River, between the Kawarau Falls Bridge and Remarkables Park.

All water users were asked to take "extreme care" when near the barges and divers.

Mr Mole said the trees were a "haven" for the invasive aquatic weed to grow and potentially spread into the lake.

"Removing the dead and submerged willows will also make it harder for the weed to hide and take hold, which helps us to keep the lake clear," Mr Mole said.

Otago Regional Council environmental monitoring and operations director Scott MacLean  supported the project.

"We know that the issue of lagarosiphon is high on the community’s priority list in terms of environmental management and it’s essential that we take all measures within our control to stop the spread of this weed."

Ongoing efforts to stop the spread of the weed were making "positive progress".

The weed had not yet gained a foothold in the lake. This was something all agencies were "determined to keep up", he said.

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