Weed washed up at the Rotorua lakefront. Photo: LDR / Ben Fraser
A funding battle is brewing over lake weed control in Rotorua as the three-week, 780-tonne clean-up of the latest stinky stranding in Lake Rotorua wraps up.
Local environmental leaders argue there is a disparity in Crown funding compared with Otago and Rotorua needs more, but the responsible agency said the South Island region gets more for good reasons.
A storm on 12 November caused masses of weed from the CBD-sized bed on the bottom of Lake Rotorua to detach, surface and collect on the foreshore.
A total of 780 tonnes of material was removed, according to Rotorua Lakes Council.
However, not before the rotting weed created a significant smell that disrupted local businesses and oxygen-depleted waters led to hundreds of dead fish.
The Bay of Plenty Regional Council began removing the weed from the water on 14 November and the Rotorua council disposed of it.
An initial estimate put the timeframe for the clean-up at 10 days, but the scale of the work and weather delays meant the operation only wrapped up last Friday, three weeks after work began.
Neither council could confirm the final cost of the clean-up operation yet.
Dead fish washing up as a result of lake weed. Photo: LDR / Ben Fraser
A 2022 wash-up cost ratepayers $35,000 to clean up.
Land Information New Zealand (LINZ) is the Crown entity responsible for lake weed management across New Zealand. It contributed $350,000 to control efforts within the Rotorua Te Arawa lakes this season.
Te Arawa Lakes Trust oversees 14 lakes and performs weed control duties.
Trust environment manager William Anaru told Local Democracy Reporting funding levels were "nowhere near enough" to find a solution to recurring stranding issues.
"For Lake Rotorua, you are talking probably needing over $1 million a year," Anaru said.
"The realistic money figure needed to actually control weeds across all the lakes is in the tens of millions of dollars a year, not hundreds of thousands."
Water conditions left Lake Rotorua unsuitable for spraying this season and budget restrictions meant the trust focused its efforts on areas of potential lake-to-lake spread, recreational activity and cultural significance.
Anaru said he believed Rotorua was not getting its fair share in the fight against invasive weeds.
"All central government agencies are constrained at the moment," he said.
Removal of lake weed at Rotorua Lakefront. Photo: LDR / Ben Fraser
"But there does seem to be an inequitable spend between what we get and what Lake Wānaka gets, for example."
LINZ provided $1m to Otago this control season to eliminate weed from Lakes Wānaka, Dunstan and Whakatipu and the Kawarau River. Canterbury received $224,000 for its three lakes, and Waikato was given $40,000 for control efforts at Lake Karapiro.
Bay of Plenty Regional Council Rotorua catchments manager Helen Creagh warned wash-up clean-up costs would continue to be the responsibility of councils.
"There is more than 300ha of lakeweed beds alone within Lake Rotorua and current investment by Linz is not sufficient to reduce the size of the weed beds," she said.
"Until investment by LINZ is increased to reduce the size of the weed beds we expect these wash-ups will continue."
Rotorua mayor Tania Tapsell labelled the regional funding disparity "favouritism" in a social media post last month and has co-signed a letter to Land Information Minister Chris Penk with Bay of Plenty Regional Council chairwoman Matemoana McDonald seeking urgent government support.
The letter raised concerns the situation was costly, lacked a long-term solution and was detrimental to local businesses and amenities. It highlighted the funding gap between Rotorua and lakes in Otago, such as Lake Wānaka.
Effective weed management is a Crown obligation under the Te Arawa Settlement Act 2006, the letter read, with Penk urged to review funding and support.
LINZ deputy head of Crown property Tracey Burton said funding decisions were based on multiple factors, including cultural and recreational impact, potential spread and the likelihood of success.
Otago's lakes were prioritised because weed was less prevalent, making prevention more urgent, she said.
"In the North Island, where multiple invasive species are already widespread, eradication is often not possible," Burton said.
"Efforts focus on reducing their impact on the community and lake users."
By comparison, lake weed was less established in the southern lakes, said Burton.
"Here, our approach is about prevention and protecting surrounding weed-free lakes from infestation."
The size and infrastructure importance of Otago's lakes also played a factor, said Burton.
"Lake Whakatipu is roughly the size of all the Rotorua lakes combined, and several support hydroelectric generation, making weed control essential to avoid disruptions to critical infrastructure," she said.
Hydroelectricity providers regularly contributed funding to "help minimise" weed impact.
LINZ had increased weed control funding for Rotorua's lakes by 40 percent since 2019, she said.
Anaru said funding was increasing but has begun to decline again. He said he will not stop advocating for more funding to clean Rotorua's lakes of the invasive pest species.
"Controlling the weed is probably the best thing we could do, as well as improving water quality, to restore the habitat for native species," he said.
"Our goal is to restore our taonga back to what they used to be."
- LDR is local body journalism co-funded by RNZ and NZ On Air.