Cause unknown for Rotorua wastewater pipe break, health warning for lakes and streams remains in place

A broken pipe at the Rotorua Wastewater Treatment Plant led to an overflow on Wednesday. Photo / Rotorua Lakes Council

Health warnings remain as Rotorua Lakes Council continues to investigate the exact cause of a broken pipe at the Rotorua Wastewater Treatment Plant.

The council was alerted to a treated wastewater overflow at 11.30am on Wednesday.

It is estimated the overflow was stopped between 10pm and midnight.

An interim repair has been done, with the leak now said to be “small” and “contained” within the plant. Reduced rainfall had also helped.

Teams from Trility, the Rotorua Lakes Council and the Bay of Plenty Regional Council responded to the leak.

The council said the impacted wastewater had been treated to a “very high standard”, but the public was still advised to avoid lakes and streams for at least 48 hours while testing continued.

“We don’t yet have the results of samples that were taken to check for contamination,” said the council’s general manager of infrastructure and assets, Stavros Michael.

Council infrastructure manager Stavros Michael says it is still waiting for test results. Photo / NZME

Sampling will continue on a daily basis, but it could take a “day or two”, Michael said.

Drinking water was not affected.

Treated wastewater is usually pumped to Whakarewarewa Forest, where it is sprayed on to blocks of land, but Wednesday’s overflow drained into Lake Rotorua via Sulphur Bay.

“It’s not possible to accurately predict the amount of the overflow, but we are confident it was seen and reported by workers on site very shortly after it appeared above ground,” Michael said.

The break was not caused by ongoing work on the wastewater treatment plant upgrades, Michael said, with an exact cause yet to be established.

“Once the damaged pipe can be fully exposed and inspected, we will have a better idea of what caused it,” he said.

“We can then determine the need for any further investigation or actions.”

Wednesday’s overflow drained into Lake Rotorua via Sulphur Bay. Photo / File

The damaged pipe is “35 to 40 years old” but had an expected lifespan of about 90 years, with Michael saying it was “not due for replacement” for many years.

“This is a very rare occurrence, and our community can rest assured that ensuring our critical infrastructure is well maintained is a priority for our council.”

About $427 million of investment in Rotorua’s water services was outlined in the council’s 2024-34 Long-Term Plan, with $167.4m allocated to wastewater services including the maintenance, renewal, and upgrade of infrastructure.

Councillors voted to establish a Recovered Water Working Group in July to assess alternatives to the current forest irrigation system and recommend a new permanent discharge method by early 2027.

The council said it was too soon to assess the impact of the break on ongoing upgrades or the potential cost of repairs.

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 Britain for eight years.

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