Recent monitoring shows large parts of Lake Wanaka remain free of the invasive weed lagarosiphon, Land Information New Zealand (LINZ) reports.
Divers have pulled more than 600 catch-bags of weeds from the Otago lake over the last year.
They also lined more than 20,000 square metres of the lake bed with hessian matting, to starve the weed of sunlight.
And at least three hectares of the lake has been sprayed with herbicide.
The National Institute of Water and Atmospheric Research (NIWA) has monitored the Lake Wanaka Aquatic Weed Management Programme’s work and confirmed it is a success.
Regional councils and local community groups have collaborated on the programme to stop the spread of the pest species and remove it from the lake.
LINZ biosecurity manager Dave Mole said native plant species were now thriving in areas previously overrun with lagarosiphon.
“The weed species is particularly effective at colonising lakes and killing off native plant species. Just one to two centimetres of plant material can be all it takes to infest an entire lake if left to take hold,” he said.
Lagarosiphon is a South African oxygen weed that was used in an aquarium tanks and surfaced in Rotorua lakes in the 1950s. It was first recorded in Lake Wanaka in 1972.
It grows up to a metre a month and at its full height can reach five metres.
The weed can cause problems for boat users and swimmers close to shore.
“Lake Wanaka is one of our most popular water spots. With the recent good weather over summer and increased use of the lake it’s particularly good news that NIWA’s inspection found good progress is being made in controlling the weed,” Mole said.
About two thirds of Lake Wanaka has been kept free of lagarosiphon, but the weed remains in the southern bays of the lake, particularly in Glendhu Bay and the Roy’s Bay area.
Project manager Marcus Girvan, of Boffa Miskell, said recreational lake use is increasing each year, so the strategy is to focus efforts in high use and boat launching areas.
The goals are to reduce the chance of people coming into contact with lagarosiphon, enhance lake users’ experience and reduce the risk of weeds spreading around the lake and across the region, Girvan said.
Lake users are asked to check, clean and dry boats and equipment, before and after every outing.
Further work to remove more lagarosiphon from the lake is planned in the next six months.
credit:stuff.co.nz