The threat to Lake Wakatipu
If the aquatic weed Lagarosiphon becomes established in Lake Wakatipu it will be very difficult to control and almost impossible to remove. The consequences will pose significant economic, amenity and environmental impacts to the community, including difficulty for commercial and recreational boating or water activities.
Lake Wakatipu has been considered weed-free, but the risk of weed spreading into the lake from boat users in the Kawarau River is high. Regular surveillance is carried out and we have found small amounts of Lagarosiphon in Lake Wakatipu in the past year and removed them. If nothing is done the risk will increase. The risk will remain high given that the weed can also be transferred by boat or trailer from other lakes or rivers.
Lagarosiphon is an unwanted organism which is capable of choking waterways, smothering native aquatic plant communities, and establishing quickly in waterways if it’s left untreated. Lagarosiphon will grow rapidly if it’s not controlled and pose safety problems for lake users by affecting underwater visibility and creates hazards for recreational activities such as swimming, fishing and water skiing.
Image of the invasive weed lagarosiphon growing on a lake floor
What we’re doing about it
Toitū Te Whenua has established the Lake Wakatipu Aquatic Weed Management Group (the Group), which is taking a number of immediate and long-term measures to prevent the spread.
Find out more about the Lake Wakatipu Aquatic Weed Management Group
Immediate action
Frankton Arm - Boat spraying operation
We’re planning a boat-based control operation using herbicide on weed in the Frankton Arm during August. Go to current and upcoming control work for details.
The purpose of this operation is to target the less invasive aquatic weed Elodea which grows extensively in the area and could be hiding Lagarosiphon infestations. Removing Elodea will greatly enhance detection of lagorosiphon plants.
The herbicide called diquat is water-safe, but as a precaution only we advise the public to stay out of the affected areas for at least 24 hours. Warning signs will be placed at public boat ramps prior to and during treatment and will be removed 24 hours after treatment.
Toitū Te Whenua will continue to carry out surveillance in the lake on a more frequent basis to spot any new infestations.
Read a factsheet about the herbicide diquat from the NIWA website (PDF)
Kawarau River - Buoys, willow removal and a checkpoint
We are working with councils to use buoys to cordon off the worse infestations of Lagarosiphon in the Kawarau River so boaties are not getting weed caught in their engines and spreading it. These will be in place indefinitely, or until infestation in the Kawarau River is controlled.
We will attempt to remove dead willows in the upper Kawarau River as they can restrict control work.
We ask that all boat users stop at the checkpoint just below the Kawarau Falls Bridge and turn their engines off. This will allow any weed fragments stuck to jet intakes or outboards to drop off.
Long-term strategy
Long-term management plan
The Group has commissioned NIWA to develop a long term management plan with solutions to reduce the risk of Lagarosiphon spreading and establishing in the lake.
What you can do
If you’re using a boat or other water vehicles from the Kawarau River to Lake Wakatipu, please turn your engine off and check your vessel at our checkpoint.
Remember to ‘Check, Clean, Dry’:
- Check: Remove any plant matter from your gear and leave it at the site (the river or lake bank), or put it in the rubbish.
- Clean: Clean all gear when moving between waterways.
- Dry: Ensure your gear is completely dry to touch, inside and out, then leave dry for at least another 48 hours before you use it.
Find out more on the Ministry of Primary Industries website
Contact
All media queries should be directed to the Group chair from Toitū Te Whenua, biosecurity manager Dave Mole by email dmole@linz.govt.nz
For information about control operations, please contact Boffa Miskell’s Biosecurity Project Manager Marcus Girvan by email marcus.girvan@boffamiskell.co.nz
For policies on Lake Wakatipu and Kawarau River, please contact the Harbourmaster on 027 434 5289 or go to the Queenstown District Lakes Council website