Published date

Boaties and visitors to Central Otago lakes are once again being asked to Check Clean and Dry all the gear they use in lakes and rivers as the summer season begins.

The invasive water weed lagarosiphon is well established in Lakes Wānaka and Dunstan. It’s building up in the Kawarau River and is more regularly being found and removed during monitoring of Lake Wakatipu.

Toitū Te Whenua Land Information New Zealand is the lead agency responsible for controlling the invasive lakeweed across these Central Otago waterways.

Diver checking hessian weed matting and lagarosiphon

Diver checking hessian weed matting, and lagarosiphon. Photo credit NIWA

Left uncontrolled lagarosiphon smothers our native underwater plants. It can take over lakes and create dense forests of sludgy weed on the water’s surface, blocking boat motors and ruining swimming.

Checking, cleaning and drying boat props and trailers, jet skis, kayaks and paddleboards, and fishing gear before and after they enter the water limits the spread of largarosiphon and other invasive weeds.

Toitū Te Whenua Biosecurity and Biodiversity manager, Tracey Burton says users need to think about the risks to the environment when moving between lakes and rivers.

“We’re so lucky to have beautiful lakes and rivers in our backyard where we can have fun and enjoy nature. These waterways are connected and our actions in one area can impact the whole lake and river system. That’s why we all need to do our bit to Check, Clean and Dry when moving between waterways.”

Advice on how to effectively clean equipment to remove weeds is available and the Otago Regional Council’s Check, Clean, Dry campaign advocates will be out and about again this summer.

The Check, Clean, Dry method

Extra care called for at Kingston and Frankton Arm of Lake Wakatipu

Lagarosiphon plants have been found growing in Lake Wakatipu in Kingston and all lake users are asked to be extra vigilent to keep Wakatipu clear and pristine. 

Toitū Te Whenua Biosecurity and Biodiversity manager, Tracey Burton says the location where plants were found during monitoring over the past two years suggests lagarosiphon has been brought into the lake on boats and jet skis launching off the beach at Kingston, the Frankton Marina and from the Kawarau River.

Ms Burton said while all the invasive weed is removed and the lake is regularly monitored the risk is enormous.

“Cleaning and drying outdoor equipment – especially motors and waterskis – before and after going into the lake is critical to retaining Lake Wakatipu as we know it. 

“We need to avoid even the smallest fragments of lagarosiphon hitch-hiking and spreading further into one of our clearest and most celebrated lakes,” she said.    

Lake Wakaptipu is considered a national treasure due to its outstanding natural, recreational, scenic and cultural values. It’s a popular tourism destination throughout the year and used by visitors and the local community for recreational activities including kayaking, swimming, boating, waterskiing and scenic trips.

“Any amount of lagarosiphon in Lake Wakatipu poses a very real and serious threat to the lake, which has been almost entirely free of this pest species,” says Ms Burton. 

Lake Wānaka locals and visitors asked to take care of weed matting

Boaties, fishers, tourism operators and recreational users of Lake Wānaka are being asked to be extra careful this summer to avoid damaging biodegradable matting installed in parts of the lake. 

Hessian matting has been laid at a number of new sites around the edges of Lake Wānaka. The matting supresses lagarosiphon while at the same time allowing native plants to grow through.  

Toitū Te Whenua Biosecurity and Biodiversity Manager, Tracey Burton says hessian matting is an invaluable tool in the fight against lagarosiphon in Lake Wānaka but it needs to be protected:

“We’re asking all lake users but especially people fishing and boating in these areas to avoid the matting where possible or take extra care not to disturb the matting in areas where it is laid.”

Lake Wānaka hessian and buoys

Around twenty red and black marker buoys are in place in Lake Wānaka to mark areas where new and recently maintained hessian matting is in place.


A buoy with the text "DANGER. Hessian below. Prop entanglement" next to a boat

Hessian marker buoy in Lake Wānaka. Photo credit NIWA

Hessian matting has been laid close to shore at: 

  • Paddock Bay
  • Sandspit
  • Glendhu Bluff Bay (including Emerald Bay)
  • Parkins Bay
  • Fern Burn (between Parkins Bay and Glendhu Bay)

“Boat operators need to avoid approaching by boat or fishing near the shore at these locations as there’s a risk of prop and fishing lure entanglement which damages the matting and ruins its effectiveness”, she says.  

Kawarau River hessian and buoys:

A line of orange buoys marks the area where hessian matting is laid on the Kawarau River. The line of buoys is intended to discourage boaties from driving between the shoreline and buoys.

The section is just after the first bend downstream of the State Highway 6 bridge (connecting Frankton and Kelvin Heights).

Check Clean Dry – it’s what we do

Ms Burton says whether you’re dipping in Dunstan, whooping it up in Wānaka or kicking about in the Kawarau it’s important you help protect and get behind lake restoration efforts.

“The presence of lagarosiphon and the risk of infestation from other water weeds such as hornwort poses a very real and serious threat to the future of Otago’s lakes,” she says.

“We use our lakes and rivers to kayak, swim, boat, water ski and take scenic trips. They are vital economic assets, supporting electricity generation and the tourism industry throughout the year and we can’t take them for granted.”

The Toitū Te Whenua annual biosecurity programme is underway across the region. To read more about the work going on to protect and restore lakes in the region visit our current and upcoming control work  

Diver swimming over hessian weed matting

Diver swimming over hessian weed matting Parkins Bay Lake Wānaka. Photo credit NIWA

For more information

To find out more about what areas are laid with hessian on Lake Wānaka please call 0800 638 943. 

MPI’s Check Clean Dry programme is the national campaign aimed at engaging communities to prevent the spread of lagarosiphon (and other aquatic pests) through checking, cleaning and drying all water sports equipment.

Keep an eye out for this year’s Check Clean Dry advocates Mandy, Jimmy and Zac from the Otago Regional Council. They will be sharing Check Clean Dry pointers and handing out some useful freebies. 

Check Clean Dry


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