LRCA AGM & Ohau Wall Public Meeting
December 13, 2025
Fix Ohau Wall – LWQS Update
December 18, 2025
LRCA AGM & Ohau Wall Public Meeting
December 13, 2025
Fix Ohau Wall – LWQS Update
December 18, 2025
Show all
4

Fix Ohau Wall – Special Public Meeting

18 December 2025

Fix Ohau Wall Background

and

Special Public Meeting to Ensure Lake Rotoiti's Water Quality is Protected

As reported throughout the year, serious concerns have emerged around official overtures regarding the integrity of the wall from both a physical perspective and its role in protecting Lake Rotoiti water quality. 

In summarising events over the year to date, it will be recalled that late last year, Bay of Plenty Regional Council (BoPRC), as the consent holder, proposed to work through repair options for the wall.  Several scientific and engineering reports provided by University of Waikato (UoW) and consultants WSP Engineering (formerly BECA) have guided the current Council position which has recommended the adoption of a Dynamic Adaptive Pathway Plan (DAPP) intended to provide a ‘flexible framework for future decision-making as new information becomes available’.  This programme has a $1.9million budget to allow for further trials and inspections over the next 12-18 months so as to inform best options for the future of the wall and lake water quality.  The decision by Councillors at their Meeting of 7 August 2025 included a rider that all relevant work should be ‘conducted expeditiously’.

Council revelations in March of this year became the major topic of presentation and debate at the Lakes Water Quality Society (LWQS) AGM resulting in a resolution ‘to pursue an expedient long-term engineered solution to the Ōhau Channel wall repairs in collaboration with the Rotoiti community in order to prevent the leakage of Lake Rotorua water into Lake Rotoiti’.

A joint Working Committee comprising LRCA and LWQS members was established soon afterwards to decide on a strategy towards effecting immediate remediation of the wall.  This resulted in the Fix Ōhau Wall campaign which has gained prominence through local media including a TV1 News item, a dedicated website, and via regular reporting back to community members.  The campaign focused on illuminating the issue both publicly and in submissions to BoPRC, as well as soliciting supporting views from other community bodies and representatives, all in a concerted effort towards a firm commitment to maintain the wall in its original condition (despite suggestions that it may no longer be relevant) and expedite remedies for its ever-increasing deterioration.

Inevitably, this pre-emptive approach precipitated rifts between our group and BoPRC with Council claiming that some of the narrative in campaign reporting could be construed as misinformation.  We have expressed confidence that our mandated content in media and website reporting has been factually based on commentary and data available from Council produced documents and reports, along with other agencies and individuals recognised as experts in the field.

To outline some of the more contentious issues arising from the dispute:-

  • Based on UoW modelling, BoPRC contends that with Lake Rotorua at or close to its target Trophic Level Index (TLI) of 4.2 over recent years, the impact of wall removal on Lake Rotoiti would lead to only a small deterioration in water quality.  This conflicts with the projection that Rotoiti’s TLI would gradually worsen.   Indeed, there is a compelling conviction within the community that the water quality target for Lake Rotorua is incompatible with Rotoiti’s target TLI of 3.5, and that retention and remediation of the Wall is considered imperative.
  • Most recent TLI data shows Lake Rotorua trending upwards. Given expected climate challenges in coming years, uncertainties around sediment locking, the ongoing likelihood of significant internal nutrient cycling, and groundwater lag effects over the foreseeable future, longer term improvements to that lake’s water quality seem highly unpredictable if not improbable.  Furthermore, recent annual reports show that Total Nitrogen (TN) loads in Lake Rotorua remain high (around twice the volumes in Rotoiti) and have not significantly declined since 2000, thereby continuing to impact Lake Rotoiti water quality.
  • Records show that Rotoiti’s TLI reduced to ≈3.4 by 2014, 6 years after commissioning of the wall.  Since the discovery of advanced corrosion from that time, the TLI has trended back upwards to its current level of 3.8, algal blooms have increased, and water clarity has declined.  No clear alternative evidence has yet been provided for this decline, giving credence to our belief that the most likely cause is re-introduced nutrient inputs via holes in the wall. 
  • BoPRC’s assertions that algal blooms in Okawa Bay and Te Weta Bay in particular are of unrelated origin to similar blooms in the Ōhau Channel have been noted.  However, a logical explanation for greater occurrences, irrespective of species, is the increasing nutrient input from wall breaches.  Recent satellite images show algae plumes entering the main body of Lake Rotoiti via those breaches.  Further studies currently being undertaken by UoW are expected to shed more light on this particular issue.
  • A peer review by two of our local resident qualified engineers of available engineering reports relating to the condition of the wall’s structural elements raises questions over some of the findings and recommendations, particularly regarding the extent of degradation.  Evidence suggests that failure rates of both king and sheet piles are likely more advanced than currently projected indicating the need for more immediate repair.  BoPRC contractors have recently carried out further inspections with assessment results likely in February 2026.

It is generally understood that the wall was intended as a finite structure with its life-span dependent upon the level of improvement in Lake Rotorua’s water quality.  Despite BoPRC asserting that current improvements attributed to enhanced catchment management practices and alum dosing, along with recent modelling of water quality, indicates removal of the wall today would likely result in only minor decline in the water quality of Lake Rotoiti, the reports from UoW can be interpreted as somewhat ambiguous and inconclusive, containing such statements as:

  • ‘even with the most ambitious reduction in maximum TLI in Lake Rotorua (i.e. 3.8), additional water quality management in Lake Rotoiti would be required to achieve the target TLI of 3.5’
  • ‘removal of the wall alongside a maximum annual TLI in Lake Rotorua of 4.2, without additional measures, will be insufficient to have Lake Rotoiti meet its TLI target of 3.5’
  • ‘The TLI in Lake Rotoiti is still above its target. There is also no clear evidence that water quality in the lake is still improving with some evidence that the TN and TP concentrations are going through a period of increase. This suggests that the continued placement of the wall is still warranted’

LRCA and LWQS representatives continue to participate as part of Council’s re-formed Rotoiti Liaison Panel (RLP) which meets periodically to work through the technical aspects of repair options available, and discuss methodologies and timing for the DAPP implementation.  Decisions from the BoPRC August meeting included a requirement to expedite investigation into further options towards improving water quality in Lake Rotoiti and Okawa Bay in particular.  Work has commenced on both fronts with updated reports due in the near future.

It is acknowledged that projected costs of long-term remediation of the wall are challenging and that decisions require robust deliberation to ensure effective interventions are delivered. Nonetheless, community frustrations have deepened over the length of time elapsed since the first discovery of corrosion in 2014 and the more recent stance adopted by BoPRC that Lake Rotoiti’s declining water quality has less relevance to the leaking wall.  In our view, the deterioration is already impacting Lake Rotoiti, and deferring action risks reversing years of environmental progress.

Moreover, there is continued belief by many in the community that on existing evidence, it is likely to remain several decades or more before water quality in Lake Rotorua might reach a stage of improvement whereby the impact on Rotoiti would be minimised to such extent that would justify removal of the Ōhau Channel Wall.

We will continue to pursue our concerns and advocate for the most optimal solutions towards the protection and enhancement of water quality in our lake and seek to work in collaboration with all agencies to reach acceptable and timely outcomes to ensure that the mauri of Lake Rotoiti is maintained for our current and future generations.

This matter will be subject to a SPECIAL PUBLIC MEETING organised by LRCA and LWQS following our upcoming AGM on Friday 2nd January 2026.  We urge everyone who is passionate about the future of our lake to make every effort to attend.

For further information and updates, visit our websites fixohauwall.nz and rotoiti.co.nz

Latest News Update from BoPRC - Ōhau diversion wall monitoring work begins

Greenfield diving contractors commenced the critical 3-year Ōhau diversion wall monitoring work on Tuesday 4 November 2025.  The work undertaken involved inspecting the wall underwater, measuring the steel thickness at multiple locations and assessing the condition of each wall component. This is critical to inform the structural analysis of the wall and Regional Council’s process to design and trial potential repair methods.

All official updates for the Ōhau diversion wall can be found on BoPRC website: The Ōhau Diversion Wall