Extremely low lake and river levels are extending weed beds out into the Kawarau River, with a risk of boats and other river users carrying lagarosiphon fragments into the Frankton Arm and other areas clear of invasive aquatic weed.

In response, additional sections of the Kawarau River from the Shotover River confluence through to the Frankton Bridge were buoyed off from river users on Saturday 21 September in order to limit the spread of lagarosiphon.

Queenstown Lakes District Council (QLDC) Harbourmaster, Marty Black said the Kawarau River was sitting at the lowest level he’d seen for some time, and that placing buoys in problem areas would provide an effective barrier and help river users keep their distance from the weed.

“We’ve placed buoys every 20 metres over an estimated one kilometre of river, and each buoy is joined by rope,” Mr Black said. “These buoys will stay in place as long as they’re required and until the river rises to an acceptable level.”

“At this stage, we ask that all river users stay away from the buoy lines and weed beds to help in preventing any further spread of this weed.”

Lagarosiphon (Lagarosiphon major) represents a threat to the high ecological, recreational, utility and monetary values of Lake Wakatipu.

The presence of lagarosiphon infestations in the upper Kawarau River between Kawarau Bridge and the Shotover River poses the greatest invasion risk, with past incursions removed from Lake Wakatipu showing a pattern associated with jet boat traffic returning from the river, indicating the role of boating as the major spread pathway for this submerged weed.

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