A lake weed harvester has been operating on weed-infested Okawa Bay in Lake Rotoiti, but residents say it's a short-term fix and more needs to be done.

The harvester, owned by the Bay of Plenty Regional Council, has been on the lake for almost three weeks and while locals say it has improved things in the short term, a long-term solution needs to be found sooner rather than later.

The issue came to a head a few weeks ago when boats taking part in the annual wooden boat parade could not travel into Okawa Bay due to large masses of weed fouling motors, keels and rudders.

Regional council senior land management officer Richard Mallinson said by the time the harvester was taken off the lake, by mid-next week, it would have gathered between 700 and 1000 tonnes of lake weed that gets taken to Kawerau for composting.


He said the harvester would then be taken back to Lake Rotoehu.

"It can do about 18 loads a day at approximately four tonnes a load.

"It's made a big difference, but we can't keep it here forever," he said.

Chairman of the Lake Water Quality Society and Okawa Bay resident Don Atkinson said the harvester had made some impact in the weed-clogged bay but described the process as "mowing a lawn with half a catcher".

"They have made a good impact, far better than if nothing had been done," he said.

Lake weed harvester pilot Scott McLaren has been pulling lake weed out of Okawa Bay in Lake Rotoiti for almost three weeks. Photo/Stephen Parker
Lake weed harvester pilot Scott McLaren has been pulling lake weed out of Okawa Bay in Lake Rotoiti for almost three weeks. Photo/Stephen Parker

"We'd like to keep out it here, but logically it has to go to other places. We are still focused on spray being applied to the bay and other bays around the lake."

He said concerned residents were still pushing for the scientifically proven herbicide Endothall to be sprayed on problem areas.

"To harvest the bay, and all the other bays around the lake, is unsustainable and unachievable.

"We've got to find an alternative, otherwise lake users and the community here are going to be very frustrated and angry.

"From our point of view, Endothall is the key.

"They have been spraying it with Diquat for 50-odd years and it hasn't done anything, in fact it's worse."

Mr Atkinson said he didn't think people were asking too much and said any long-term solution would cost money.

"But to say it's too hard is not acceptable," he said.

"We are asking for a higher standard of care.

"We are going backwards on this."

Mr Mallinson said spraying the entire lake was not cost-effective and could cause algal blooms.

He said the spray Endothall had not been proven on large bodies of water and was expensive to use, but he agreed that a long-term solution was necessary to control weed issues in the lake.

"We do a limited amount of spraying and use the weed harvester to tidy up.

"But we can't get all of it, so there will still be weed washing up outside people's properties."

Attempts to contact Te Arawa Lakes Trust chairman Sir Toby Curtis and deputy chairman Willie Emery for comment were unsuccessful.

-Visit www.rotoruadailypost.co.nz for video of the harvester in action and more comments from Richard Mallinson.