The efforts to manage lagarosiphon at the popular Otago lake are part of Toitū Te Whenua Land Information New Zealand’s (Linz) annual biosecurity programme.
It also does lagarosiphon removal work on Lake Wānaka with the ultimate goal of clearing that lake of the invasive weed.
Lagarosiphon has been in Lake Wānaka since the 1970s while Lake Dunstan was only formed in the mid-1990s when the Clyde Dam came into operation.
Linz biosecurity manager Tracey Burton said eradication was not an option in Lake Dunstan as the weed was spread into the lake from upstream sources in both the Clutha and Kawarau Rivers.
‘‘Our goal for this work is to reduce the risk of lagarosiphon being spread to other water bodies within the Otago region,’’ she said.
Lagarosiphon can form dense, surface-reaching weed beds that can grow up to five metres tall. It grows fast and can invade new water bodies quickly — a fragment the size of a fingernail is all it needs to spread.
‘‘This year we will be continuing control work at sites that have been identified as high-risk areas and high amenity areas.
‘‘High-risk areas include boat ramps, as these are often sites where lagarosiphon can be removed from the lake, as well as where potential new weeds or pests can enter. High amenity areas include popular spots like the Cromwell swim beach.
She said divers would be hand cutting the weed in the lake, with particular attention paid to boat ramps and swimming areas.
“This work will build on efforts late last year to make sure lake users can enjoy the lake over the summer period.
“Lagarosiphon can take over lakes, choke waterways, smother native aquatic plants and impact how we use our lakes so it’s important we keep it in check and prevent it from spreading to other areas.“
The control work is expected to take around two weeks and be finished later this month.
She said lake users could also play a part in helping stop the spread of aquatic weeds by checking, cleaning, and drying all gear.
“We must be more vigilant than ever in our inspections. While Lake Dunstan is already affected by lagarosiphon, we need to protect it from other freshwater pests, such as New Zealand’s worst submerged weed, hornwort, and other pests like the gold clam currently only in the North Island”.
The control work will be carried out by Linz biosecurity delivery partners Boffa Miskell.
— APL
