AUTHORITIES fearing damage to Lake Wakatipu are closely monitoring a swamp-like weed infesting Queenstown’s Kawarau River.
An inspection earlier this year found several clumps of the noxious weed lagarosiphon just a kilometre from the river mouth.
An Otago Regional Council compliance committee report says there’s a high risk of the clusters “being a source for re-infesting Lake Wakatipu”.
The weed was discovered and removed from the lake in 2007 and has not been found there since.
But the report warns: “With Lake Wakatipu seen as a pristine lake with high tourist and visual status, establishment of this water weed would be a major loss to the local community as well as New Zealand.”
A plan is needed to assess if eradication is feasible, the report adds – but experts are baffled about how to do this because of the Kawarau’s fast flow.
A dredging technique or chemicals are usually used to remove it, but swift currents are preventing this. There are also dangers for divers helping with any removals due to fallen trees hidden under the water.
ORC service manager Jeff Donaldson says Lake Wakatipu’s shorelines could become a “swampy breeding area” if re-infested and left uncontrolled.
“If it gets into the marina in the Frankton area it would cover right across from there to the river – it would completely take over the area.”
Lagarosiphon can grow in up to eight metres of water, making swimming virtually impossible. It also tangles in boat propellers and fishing lines. Donaldson believes the river’s current will prevent it from moving upstream by itself, so for now regular checks are in place.
Queenstown harbourmaster Marty Black suggests people should clean and check all recreation gear before moving between the region’s lakes to prevent the weed spreading.