Wanaka Sun       

Boaties beware of hessian matting

Posted at 5:05am Thursday 27 Dec, 2018 | By Ruth Blunt editor@thewanakasun.co.nz


This summer boaties on Lake Wanaka  are being asked to take extra care to avoid tearing the hessian matting which has been laid on the lakebed to tackle the spread of the lake weed lagarosiphon.
“We're asking anyone using a boat to lift their prop out of the water as they near the beaches where hessian has been laid,” Boffa Miskell's Marcus Girvan said.
He said matting can be found in parts of Paddock, Parkins, Glendhu and Roys Bays, and at Stevensons Island, and has proved to be an effective tool for killing off the invasive weed and preventing its spread.
Lagarosiphon can grow up to 4m in length and spreads rapidly, displacing native plants and making swimming and other water-based leisure activities less pleasant.
Lake Wanaka is one of just three lakes in New Zealand to have the matting. The relatively flat lakebed means divers can easily lay the matting which smothers the weed while allowing native plants to grow through the weave.
Land Information New Zealand has been leading the effort to tackle lagarosiphon in Lake Wanaka.

“We've done quite a bit of experimenting with the type of hessian,” LINZ biosecurity director, Dave Mole, said.
“Inspections by NIWA have shown the positive impact it's having on the lake's ecosystem. But because it's biodegradable it does mean it can easily tear and get caught in boat props, which is why we're putting up signs around the lake asking people to take care over the busy summer period.”
Girvan said the use of biodegradable hessian has been a game-changer.

“Although it's relatively expensive at around $60,000 per hectare, once it is laid very little follow up control is required, which will reduce our reliance on herbicides in the long run.”
The hessian was first trialled here over two years ago and, as a result of its success, it is now being used extensively in the lake and elsewhere in the South Island.



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