Testing eases Rotorua lake and forest 'forever chemical' fears

The Rotorua Lakes Council is celebrating two environmental wins.

It says testing has found no evidence of "forever chemicals" contaminating aquatic life in Lake Rotorua, nor significant ecological damage linked to more than three decades of treated wastewater irrigation in Whakarewarewa Forest.

The trust that owns the lakebed has stopped short of giving the lake the all-clear, while another council plans further testing.

It comes as the process to decide how to dispose of Rotorua's treated wastewater in the future ramps up.

The council's infrastructure and assets manager, Stavros Michael, told councillors the "good news" at an infrastructure committee meeting on Wednesday.

He said initial testing in kākahi at Lake Rotorua had shown "no bioaccumulation" related to the historic use of PFAS-containing firefighting foam at Rotorua Airport.

PFAS – or per- and polyfluoroalkyl substances – are commonly known as forever chemicals.

In August, it was confirmed PFAS were entering the lake, prompting concerns about potential impacts on mahinga kai (traditional food gathering) species.

Lakebed owner Te Arawa Lakes Trust expressed caution after the update.

General manager Tame Malcolm told Local Democracy Reporting that while "some testing" may have been promising, regular users should not be complacent.

"Marae and hapū around the lake will still need to assess the risk associated with any activities in and on the water," Malcolm said.

"Therefore, we encourage the relevant agencies to meaningfully engage directly with them."

Further testing to fully understand the potential ecological impacts of such chemicals on the lake is set to continue, with Bay of Plenty Regional Council approving a $30,000 investigation last month.

It was also cautiously optimistic about the results.

"The scope and sample size of the data set is too limited to make any general conclusions about the extent and levels of contamination in Lake Rotorua," a regional council spokesperson said.

They said it was "positive" that materials were not detected at the control sample locations and that these initial results would help inform the "design and development" of their future investigation.

Forest irrigation all-clear

Monitoring has also confirmed the 35-year practice of irrigating treated wastewater into a section of Whakarewarewa Forest has not caused any significant environmental harm.

It comes as the council moves into the final stages of commissioning its $60 million upgraded wastewater treatment plant.

Soil contamination studies at the site showed levels of heavy metals, PFAS and other forever chemicals were "hundreds of times below" the threshold at which they would be considered hazardous, Michael said.

The findings showed concerns about long-term human health impacts from the practice were "not substantiated", he said.

Since 1991, Rotorua has sprayed treated wastewater on to a section of the forest instead of discharging it directly into Lake Rotorua.

In 2013, the council was directed to find an alternative by 2019. After no replacement was identified, a 2020 agreement allowed temporary discharge on to a reduced 40ha area of the forest while the council worked towards a permanent solution.

That solution now appears to be within reach.

Wastewater programme manager Ian Gray told elected members the treatment plant was nearly complete and on track to begin producing fully treated recovered water in early 2027.

Nine options for managing the recovered water remain on the table, with one final meeting of the council's Recovered Water Management Solution Working Group scheduled for next month.

Councillors are expected to consider one or two preferred options in December, and then decide which to put out for public consultation through the council's long-term plan process.

A final decision is expected in June 2027, aligning with the council's application for new resource consents and the future management of the city's recovered water.