Sections of the Upper Kawarau River have been cordoned off with buoys to restrict the invasive oxygen weed (lagarosiphon) from spreading and all river users are being urged to help prevent the weed from emerging in Lake Wakatipu and the Frankton Arm.

The Lake Wakatipu Aquatic Weed Management Group, commercial river users and the Jet Boat Association have agreed on immediate actions with the top priority being to keep the weed out of Lake Wakatipu.

Queenstown Lakes District Council Harbourmaster Marty Black says as part of the action plan all commercial companies and jet boat drivers are required to keep clear of all weed beds until further notice.

“River cordons have been installed to make it obvious where the out of bounds area is.

“Drivers will also notice signage advising jet boat drivers to switch off their engines before they head under the Kawarau Falls Bridge and into the lake. Switching off the engine will help weed drop from the jet unit and limit the weed spreading.

“Everyone who uses the lake needs to know that human activities are the major factor in the spread of lagarosiphon through the accidental transfer between waterbodies on contaminated boating or fishing gear.”

If it’s not controlled, lagarosiphon is capable of choking waterways, smothering native aquatic plant communities, and establishing quickly in waterways. This can also pose safety problems for lake users by affecting underwater visibility and creates hazards for recreational activities such as swimming, fishing and water skiing.

Mr Black adds “there are straightforward things people can do to help prevent the spread of lagarosiphon, such as checking boats and other craft for weed fragments after using them in the lake.

“Lake users should also hose down and dry all equipment such as water skis, biscuits or fishing gear.  This is crucial if lake users are planning to move between launching sites, waterbodies or catchments.”

There are three river cordons set up (see attached map).

The ramp below the bridge that can be accessed via SH6 will also be closed.

Commercial operators, KJet and Thunder Jet, have both agreed to help clear submerged willow branches from the banks of the river as this inhibits further weed control.

ENDS

 

Locations of the river cordons:

• First is 200 metres at top of the bend diagonally out into the river and opposite the first 5 knot buoy (river channel in between )
• Second section is 100m downstream and is set to block off entry into Big Beach
• Third section is 100m and anchored to the bottom 5 knot buoy  from the Zoological Gardens, on the upstream side it is anchored back to the beach to deter boats entering the last large bed of weed on their way back up the river.

 

What is Lagarosiphon?

Lagarosiphon (Lagarosiphon major), —or South African oxygen weed—was originally used by the aquarium trade.  It was first noticed in the Rotorua Lakes in the 1950s and since then has gradually appeared in many lakes, often as a result of spread by recreational users. It was first discovered in the Kawarau River in 2008.

Lagarosiphon can reproduce from very small single fragments of the plant.  If plant material is transported to a waterway with no lagarosiphon, it may find suitable habitat and send down roots and regrow.

 

Note: The Lake Wakatipu Aquatic Weed Management Group is made up of representatives from Queenstown Lakes District Council, Land Information New Zealand, Otago Regional Council, Ministry for Primary Industries and Department of Conservation and operate advisory services of the National Institute of Water and Atmospheric Research and Boffa Miskell.