Clampdown on invasive weed begins in Kawarau River

A major operation is underway in the Kawarau River to protect Lake Whakatipu, with targeted action to eradicate lagarosiphon – one of New Zealand’s most invasive freshwater weeds.

Around 60,000 square metres of hessian matting – roughly the equivalent of eight rugby fields – is being laid across sections of the riverbed to suppress the weed, marking a significant push to remove lagarosiphon from the river, says Toitū Te Whenua Land Information New Zealand (LINZ) Leader Biosecurity Tracey Burton.  

“This work is fundamentally about protecting Lake Whakatipu,” says Burton.  

“The Kawarau River is the primary pathway through which lagarosiphon could spread into the lake. By focusing on eradication here, LINZ is cutting off that risk at the source and giving Lake Whakatipu the best possible protection – now and into the future.”
 

Minister for Land Information Mike Butterick is visiting sites where LINZ is undertaking control works in the Central Otago region today.  

This is a significant and practical step to protect one of New Zealand’s most iconic lakes,” says Minister Butterick.

“Preventing the spread of invasive species like lagarosiphon is critical to preserving our natural environment, and will deliver real benefits for local communities, businesses, recreational users and the wider ecosystem.”
 

Lagarosiphon is one of New Zealand’s most damaging freshwater weeds. It grows quickly, forming dense surface reaching weed beds, and can choke waterways, smother native plants, restrict recreation, and degrade lake and river ecosystems if left unchecked.

Hessian matting acts like an underwater shield, smothering the weed while allowing native vegetation to re‑establish. The technique is being used alongside hand weeding in carefully targeted areas to maximise the chances of fully removing the weed from the river system.

“Protecting Lake Whakatipu also relies on the actions of the wider community,” says Burton  

“I want to acknowledge lake users who have been diligent about checking, cleaning, and drying their gear, and encourage everyone to keep that up.”