Threat of weed to Qtown lake grows
Fears an invasive weed will establish itself in Queenstown’s Lake Wakatipu are escalating as crops continue to spread in a river that drains the lake.
A large-scale, collaborative operation, including spraying, will be undertaken on Frankton Arm in August to detect lagarosiphon and prevent its spread into Lake Wakatipu. Boaties will also be required to stop at a checkpoint and turn off their engines.
Land Information New Zealand (Linz) senior portfolio manager biosecurity Dave Mole said the potential for the invasive weed establishing itself in what was considered currently a ‘‘weed-free’’ lake was ‘‘very, very high’’, and once established would be almost impossible to remove.
The weed was already established in Lake Wanaka, Lake Dunstan and was growing in the Kawarau River which drains Lake Wakatipu and flows through a gorge to Lake Dunstan, in Cromwell.
Linz had established the Lake Wakatipu Aquatic Weed Management Group, which was taking several immediate and long-term measures to prevent the spread, he said.
‘‘There is no question – the threat is real.
‘‘The consequences will pose significant economic, amenity and environmental impacts to the community, including difficulty for commercial and recreational boating or water activities.’’
Lagarosiphon was capable of choking waterways, smothering native aquatic plants, and establishing quickly in waterways if left untreated, he said.
‘‘Lagarosiphon will grow rapidly if it’s not controlled and pose safety problems for lake users by affecting underwater visibility and creates hazards for recreational activities such as swimming, fishing and water skiing.’’
Lake Wakatipu was considered weed free, but the risk of weed spreading into the lake from boat users in the Kawarau River was high, Mole said.