The removal of more than 150 tonnes of submerged trees from the Kawarau River near Frankton will allow divers to remove an invasive weed in a follow-up operation next year.
In a nearly three-week operation completed last month, a 24-tonne excavator was floated up the river on a barge to remove the trees.
Focused mainly on the true right or Peninsula Hill side of the river, the operation started about 700m from the new Kawarau Falls bridge and extended more than 500m downstream.
The operation’s $111,000 cost was funded by Land Information New Zealand (Linz) and the Otago Regional Council (ORC). Contractor Boffa Miskell carried out the work.
Boffa Miskell biosecurity project manager Marcus Girvan said the submerged willow trees and branches were a "dense jungle" that had made it too risky for divers to carry out work to remove the invasive weed lagarasiphon.
The matting killed the plant by shading it from the sun. Linz biosecurity director Dave Mole said the "very difficult" operation had paid off, and the biodegradable matting would "massively" curtail the growth of lagarosiphon and allow native vegetation to flourish.
The wood has been chipped into mulch and given to the nearby Zoological Gardens.
Co-owner Rachel Young said the mulch was a "fantastic bonus".
"The organic mulch will be used in our wildflower garden as plant-starting material, and represents a huge cost saving for us."
