Around four rugby fields worth of hessian mats will be laid on the floor of Lake Wānaka to help eradicate lagarosiphon from the lake in a project which began yesterday (Wednesday February 26).

The two-month project will build on progress made over the past 20 years to clear lagarosiphon from the lake’s shoreline, led by LINZ.

“The initial focus of divers will be monitoring the weed-free part of the lake and hand weeding any isolated plants,” LINZ biosecurity manager Tracey Burton said.

“They will then turn their attention to controlling the weed outside of the weed-free area, working their way away from the western side of the lake towards Roys Bay, near the township."

“In this part of the lake, divers will install around 4.5 hectares of hessian mats to smother the weed.”

Tracey said it is essential to control lagarosiphon as it can take over and choke waterways, smother native plants and affect the way lakes are used.  

The ultimate goal continues to be eradicating lagarosiphon from the lake, she said.

“We’ve made good progress over the last few years, and we’re excited to see what impact we can make this season,” Tracey said.

“We’re hopeful these efforts will enable us to clear the weed from more parts of the lake and enable us to move the containment line further towards the township as we push to progressively clear the lake.” 

A map of Lake Wānaka showing the containment line that shows the weed-free areas in the lake and areas infested with lagarosiphon. IMAGE: Supplied

The containment line represents the divide between weed-free areas in the lake and areas infested with lagarosiphon, and it currently stretches from the southern point of the peninsula to the southern point of Bishops Bay.  

The goal this season is to move the containment line further south to include Paddock Bay, Parkins Bay and Glendhu Bay in the weed-free areas.

“Little by little we’re pushing the containment line out and we’re hopeful we can do that again with these continued efforts.”

The control work will be carried out by LINZ biosecurity delivery partner Boffa Miskell Limited and it is partly funded by Queenstown Lakes District Council.

Lake users are asked to be aware of the dive flags and to avoid the area, if possible.