Rotorua lakefront stench lingers as seaweed and dead fish pile up

Something stinks in Rotorua, and it’s not the sulphur scent locals embrace and visitors expect.

Rotting lake weed is casting a funky fog over the city’s lakefront as a 70 tonne-a-day clean-up of Lake Rotorua continues.

Businesses in the area say the stench is so bad that customers are complaining or staying away.

The washed-up weed is also causing piles of dead fish to surface.

Some in the community are calling for more investment in weed control to prevent the mess from happening again and protect Rotorua’s reputation.

It has been two weeks since strong winds caused masses of weed to surface from the lakebed and collect on the foreshore.

The Bay of Plenty Regional Council began removing the washed-up weed from the water on November 14, with Rotorua Lakes Council disposing of it once removed.

The clean-up was delayed last week by heavy rain – but the bad weather coming sandwiched between warmer days has only exacerbated the weed’s putrid pong.

Wai Ariki Hot Springs and Spa general manager Debbie Guptill said she was “deeply concerned” about the smell.

“It’s had a significant impact on the experience of our guests and the overall perception of the lakefront as a premier destination,” Guptill said.

“We are receiving ongoing negative guest feedback regarding the odour, and we urge that a solution be prioritised to ensure Rotorua continues to deliver the world-class visitor experience it is renowned for.”

Lime Cafe head chef Rohan Jalota said the business had no choice but to keep the cafe doors closed during opening hours, making conditions inside “very hot”.

“It has affected us because it is a very bad smell and we have definitely lost customers because of it.”

Regional council lakes operations officer Justine Randell said “unpleasant odours” were expected as the weed begins to decompose, particularly during warm, favourable weather.

The clean-up, which involves a weed harvester operating on the lake, was initially expected to last 10 days but Randell said it was likely to continue for the rest of this week.

She said 20 harvester loads, roughly 60-70 tonnes, of weed were being removed a day.

“We will assess progress later in the week as to whether the harvester will work into next week,” she said.

“We are working with Rotorua Lakes Council as fast as we can to remove the weed.”

Rotorua Lakes Council parks and open spaces manager Rob Pitkethley said he was aware the smell was “unpleasant” but work was moving as “quickly as possible”.

“The day the regional council’s harvester wasn’t able to work because of bad weather we were still able to truck weed away,” he said.

As much as 80 tonnes of removed weed was transported to EcoGas’ Reporoa site, where it is being used for energy generation.

This is not the first time Rotorua has faced this problem – in 2022, 300 tonnes of weed was removed at a cost to ratepayers of at least $35,000, and the “rancid” smell issue also resurfaced last year.

Regional council biosecurity officer Te Wakaunua Te Kurapa said the dead fish floating to the surface was due to “oxygen-depleted waters” caused by the weed.

Te Kurapa said the situation was unlikely to change without better investment into addressing the underlying problem – an underwater weed bed larger than Rotorua’s CBD.

“It extends from Kawaha Point and eastward to Te Kaunanga (Sulphur Bay) covering an area of approximately 300ha,” Te Kurapa said.

Storm events with strong northerly winds can “detach” masses of weed from the bed, resulting in weed strandings.

“Effectively managing the invasive aquatic weed problem in Lake Rotorua will require a significant increase in investment to scale up existing management efforts and to explore and implement new, more effective control tools,” he said.

Without that investment, more weed wash-ups were inevitable, he said.

Land Information New Zealand (LINZ) is the lead central government agency responsible for managing weeds in the lake.

LINZ biosecurity leader Tracey Burton said multiple agencies were involved in making decisions on weed control including councils, the Department of Conservation and the Te Arawa Lakes Trust – which owns the lakebed.

“With limited resources available, priority is given to boat ramps, sites of cultural and recreational significance, and areas where weed wash-up onshore poses a risk,” Burton said.

The weed was mainly controlled using herbicide and mechanical harvesting.

Herbicide, however, was ineffective this year as lake water was “too turbid”, Burton said.

LINZ has contributed $350,000 toward the control of invasive lake weed across Rotorua this control season.

The cost of using the weed harvester for the current clean-up was estimated at up to $50,000, but the final figure depended on how long it took.

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