Hessian matting is 'a game-changer' in Lake Wanaka

The hessian was first trialled in Lake Wanaka 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.

It's being used closer to the shoreline this summer, so boaters need to take extra care to avoid tearing the matting on the lakebed.

“Hessian matting has proved to be a really effective tool for killing off the invasive plants and preventing them from spreading across Lake Wanaka," says Boffa Miskell biosecurity consultant Marcus Girvan.

"This summer, the matting can be found in parts of Paddock, Parkins, Glendhu and Roys Bays, and at Stevensons Island. 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."

Lagarosiphon can spread quickly, outperforming native plants and clogging up waterways. It can get in the way of boats and is unpleasant for swimmers. Boffa Miskell and Land Information New Zealand (LINZ) have been leading a concerted effort to tackle the weed.

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, smothering the lake weed whilst allowing native plants to grow through the weave.

“We’ve done quite a bit of experimenting with the type of hessian,” adds LINZ Biosecurity Director, Dave Mole. “Inspections by NIWA have shown the positive impact it’s having on the lake’s ecosystem."

“The use of biodegradable hessian has been a game-changer at Lake Wanaka,” says Marcus.

"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 reliance on herbicides in the long run.”