Lake Rotorua: Rotting lake weed stinking up redeveloped lakefront to be removed

A clean-up will start Thursday and Friday to remove what's left of washed-up weed causing a stink at the newly developed Rotorua lakefront.

The clean-up is a joint effort between Te Arawa Lakes Trust, Toi Moana Bay of Plenty Regional Council and Rotorua Lakes Council.

The weed was washed ashore by high winds in Cyclone Dovi, however, an initial clean-up using a purpose-built lake weed harvester was hampered by low summer lake levels.
Much of the weed in shallow areas was not able to be recovered by the harvester.

It is hoped this week's clean-up will round up most of the weed that can be reached from the lake edge and is creating an odour. A digger will be used from the shore, to avoid contact with the lakebed.

The stinky lake weed at Rotorua's new lakefront. Photo / Andrew Warner

The Rotorua Daily Post reported at the end of last month the smell was impacting businesses in the area.

The cafes and bars were not only having to cope with reduced customers as a result of the Covid-19 pandemic but many couldn't stand the smell outside.

Lake weed on the $40 million lakefront redevelopment had, at that time, cost ratepayers about $20,000 to clear.

Lime Cafe manager KV Ranwat told the Rotorua Daily Post today it would be great if it could be cleaned up as soon as possible.

"We are still regularly having customers coming inside telling us they can smell it ... If they need a hand to clean it up we are happy to help. The sooner it gets done the better."

The stinky lake weed at Rotorua's new lakefront. Photo / Andrew Warner

Staff from Te Arawa Lakes Trust would be on hand to help with manually moving weed into the digger reach area. Rotorua Lakes Council staff would retrieve the weed from the lake edge and dispose of it.

The work might also cause a smell near the site for a few days.

Toi Moana Bay of Plenty Regional Council lakes operations manager Andy Bruere said weed was always in the lake, however, when exposed to shallower waters it could become a problem for lake users.

Rotorua Lakes Council's sport and recreation and environment manager Rob Pitkethley said more than 300 tonnes of weed had already been removed by the harvester, and some had naturally dissipated.

"It will be good to remove as much as possible of what's left so people can continue to enjoy our redeveloped lakefront and we'll keep working with our Rotorua Te Arawa Lakes Programme partners on plans for dealing with any future occurrences," Pitkethley said.

Environment manager for Te Arawa Lakes Trust Nicki Douglas said the pest weed bed it was working to remove was over a traditional koura bed.

"We are hoping to see the recruitment of native plants, establishing habitat for koura on the lakebed as a result of the removal of this weed."

A plan was being formulated to ensure a more streamlined clean-up for any future lake weed stranding.

The stinky lake weed at Rotorua's new lakefront. Photo / Andrew Warner

This includes obtaining consent to allow the weed harvester and an excavator to work together.

Douglas said a solution the trust intended to investigate was to plant a raupō belt across the bay to catch the dispersed weed.

The stinky lake weed at Rotorua's new lakefront. Photo / Andrew Warner

Meanwhile, yesterday a health warning was issued after satellite imagery and visual assessments revealed extensive algal bloom throughout much of Lake Rotorua.

Toi Te Ora Public Health issued the warning after information provided by the regional council indicated the spread of algal bloom.

Toi Te Ora Public Health medical officer Dr Neil De Wet said it was important to avoid any activity that could lead to contact with the lake water. Dogs were particularly at risk as they ate the blooms and should be kept away from shorelines.