Cleaning up Rotorua’s massive lake weed wash-up late last year cost local councils a combined $133,443.
By Mathew Nash of Local Democracy Reporting
A review into funding for lake weed control is now underway, with local leaders saying more needs to be done to prevent a repeat event.
A bed of invasive lake weed, roughly the size of Rotorua's CBD, lies beneath Lake Rotorua. On November 12, bad weather dislodged large amounts, leaving about 780 tonnes of material to be cleared from the lake surface.
The decaying weed produced strong odours affecting nearby businesses, while low oxygen levels in the water killed hundreds of fish.
Bay of Plenty Regional Council began skimming the weed on November 14, with Rotorua Lakes Council managing disposal. A job initially expected to take 10 days stretched to three weeks because of the scale of the task and weather delays.
Rotorua Lakes Council contributed $67,443 to the clean-up, while the regional council spent $66,000.
By comparison, clearing a 2022 wash-up cost about $35,000.
Lake weed is managed using funding from Land Information New Zealand (LINZ).
The Crown entity contributed $350,000 to Rotorua Te Arawa lakes this season, while allocating $1 million to Otago.
Te Arawa Lakes Trust oversees 14 lakes and performs weed control duties for Lake Rotorua.
Trust environment manager William Anaru told Local Democracy Reporting last month that a solution for Lake Rotorua would likely cost more than $1m a year.
Rotorua Mayor Tania Tapsell called the funding disparity “grossly unfair” and last month co-signed a letter with the regional council’s chairwoman, Matemoana McDonald, to Land Information Minister Chris Penk seeking urgent Government support.
“Our message is clear: Rotorua lakes need fair funding from Government to address significant lake weed issues,” Tapsell told Local Democracy Reporting.
She said councils, iwi and local communities had spent years developing solutions, but funding remained inadequate.
Tapsell warned recurring wash-ups were damaging for residents, businesses and visitors
"We won’t stop advocating until an appropriate solution is in place to protect Rotorua’s environment, reputation and economy," she said.
Regional council biosecurity team leader Te Wakaunua Te Kurapa described current funding as "insufficient".
Despite repeated attempts to raise concerns with Linz, he said the agency was "not fulfilling its obligations" under the Te Arawa Lakes Settlement Act.
LINZ representatives previously stated that southern lakes are prioritised as eradication is often unlikely elsewhere, where invasive weed is widespread. Efforts instead focused on impact reduction rather than eradication.
Te Kurapa disagreed. "With the right investment and resources, large-scale weed control can be achieved," he said, citing a business case established last August.
Penk said he was "actively reviewing" funding arrangements and lake weed costs compared to other regions.
"This will provide perspective on the expense Rotorua has had to meet," he said.
He said that as discussions remain underway he could not rule anything “in or out” regarding changes in support, but recognised the cost of the clean-up and its impact on the community.
"I have heard clearly the community's frustration over the impact of lake weeds on Rotorua," Penk said.
He was hopeful of meeting with Tapsell to discuss the issue now the summer break was over.
LINZ biosecurity leader Tracey Burton said several control methods for lake weed are used, but no single approach works in all conditions.
In agreement with the Bay of Plenty Aquatic Pest Coordination Group, herbicide was not considered to be an effective option this season, Burton said.
She said Lake Rotorua’s shallow profile and extensive lakebed growth make it “difficult to manage” with winds, currents and turbid water all issues.
"While we understand the frustration and costs involved in clean-up efforts, these challenges highlight the importance of continued collaboration and strategic planning to manage aquatic weeds as effectively as possible with the resources available," Burton said.
After November’s letter, council leaders met with LINZ representatives in mid-December.
Burton said the meeting was "productive" and all parties were "committed to working together" on control efforts.
An agreement was reached on investigating modelling options for weed movement during storms to enable targeted control in the hope of reducing large wash-ups.
Local Democracy Reporting is local-body journalism co-funded by RNZ and NZ On Air.
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