Rotorua lake weed clean-up could take 10 days and cost $50,000

A multi-agency clean-up to clear Lake Rotorua and the waterfront boardwalk of lake weed is expected to last beyond next week.

Wind gusts reached about 80km/h on Wednesday, driving a large amount of weed onto the foreshore and Rotorua Lakefront boardwalk area.

The Bay of Plenty Regional Council is leading the removal work on the water.

The Rotorua Lakes Council is responsible for disposing of the material once it hits land.

Image 1 of 10: Weed build up at Rotorua Lakefront. Photo / Ben Fraser

Both councils say the rapid build-up was weather-driven and not unusual for this time of year.

The regional council is using its weed harvester to do the clean-up.

Lakes operations officer Justine Randell said this could “take up to 10 days” as they are dealing with a “significant volume” of weed.

Randell said the two councils would work together on the lake weed’s transportation and disposal.

The cost of operating the weed harvester could be as high as $50,000, including disposal, but Randell said the council would not be able to confirm figures until after the clean-up.

Weed build-up at Rotorua Lakefront. Photo / Ben Fraser

District council parks and open spaces manager Rob Pitkethley said it was “not possible” to estimate the cost for disposal at this early stage.

“It depends on the volume of weed that needs to be disposed of,” Pitkethley said.

Once collected, contractors will take the weed to an area at Motutara Point on Lake Rotorua.

It will then be collected and taken by EcoGas to its Reporoa facility for “energy generation,” Pitkethley said.

This is not the first time windblown lake weed has caused issues at Lake Rotorua.

In 2022, 300 tonnes of weed was removed, costing ratepayers $35,000 and last year the “rancid” smell had out-of-towners and locals alike pinching their noses.

Regional council biosecurity officer, Te Wakaunua Te Kurapa, said this would not be the last event either.

“We will continue to experience lake weed wash-up after severe weather events,” Te Kurapa said.

He also advised residents not to dispose of lake weed in general refuse, wheelie bins or garden waste bins.

Weed washed up at Rotorua Lakefront following Wednesday night's wild weather. Photo / Ben Fraser

“This is a pest species and must be handled and transported correctly.

“The best option for people who come across the weed on the foreshore right now is to push it back into the water where it can break down naturally.”

Under the Bay of Plenty Regional Pest Management Plan, the public cannot remove lake weed from its location.

“Private lakefront property owners who want to remove the weed from their properties can contact Te Arawa Lakes Trust to arrange for weed removal at their own cost,” Te Kurapa said.

Alternatively, they can refloat the weed themselves, ideally in southerly wind conditions.

The MetService forecast for Lake Rotorua suggests westerlies on Saturday, southwest then northeast winds Sunday, staying northeast Monday and strengthening on Tuesday.

Mathew Nash is a Local Democracy Reporting journalist based at the Rotorua Daily Post. He has previously written for SunLive, been a regular contributor to RNZ and was a football reporter in the UK for eight years.

- LDR is local body journalism co-funded by RNZ and NZ On Air.