Lakeweed control to begin on Otago lakes

Efforts to control the invasive lakeweed lagarosiphon are ramping up across Otago lakes, with preparations underway for the summer season.

Divers started work at Lake Wakatipu this week, conducting monitoring and hand weeding. Over the coming weeks, they’ll focus on Frankton Marina as part of a wider programme to protect the region’s waterways.

The control efforts are part of Toitū Te Whenua Land Information New Zealand’s (LINZ) annual Otago Lakes biosecurity programme.

LINZ Biosecurity Manager Tracey Burton says controlling lagarosiphon is vital to prevent its spread and protect Otago’s lakes. 

“We’re proud to have helped keep Lake Wakatipu largely free of lagarosiphon, and we’re committed to keeping it that way.

“If lagarosiphon were to establish in Lake Wakatipu it would be extremely difficult to remove and could have significant environmental, economic and recreational impacts.”

She says one of the biggest risks of spreading the weed into the lake is boats travelling from the Kawarau River.

“We ask boat users to do their bit by turning off their engines at the checkpoint just below the Kawarau Falls Bridge. This simple action helps dislodge any weed fragments and prevent them from entering the lake.”

Lagarosiphon can quickly dominate freshwater ecosystems, choking waterways, smothering native aquatic plants, and impacting recreational use. 

The work at Lake Wakatipu is expected to take a couple of weeks.

Next, divers will begin at Lake Wānaka in mid-October, to check eradication zones, hand remove any newly established weeds, repair hessian matting, and carry out control in high-use areas. 

Control works will also take place at Lake Dunstan from mid-November and Kawarau River in late November.

Further control efforts will take place across the lakes between February and May 2026. 

LINZ is working in partnership with community groups, and organisations including Contact Energy, Otago Regional Council, and Queenstown Lakes District Council, who provide additional funding support for the work.

Burton says lake users also play a crucial role in protecting lakes by following the ‘Check, Clean, Dry’ steps – especially when moving between waterways.

These efforts in Otago are part of LINZ's wider aquatic weed control programme, which also involves work at key lakes in South Canterbury and Waikato.

Main image: Diver hand weeding lagarosiphon. Photo / NIWA