Fix Ohau Wall – Special Public Meeting
December 14, 2025
Fix Ohau Wall – Special Public Meeting
December 14, 2025
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Fix Ohau Wall – LWQS Update

18 December 2025

The satellite image above taken on the 9th December 2025 showing the extent of algal blooms in Lakes Rotorua and Rotoiti (the bright green areas in the Lakes indicate algal bloom conditions).

Update on the Fix Ohau Wall Campaign from the LWQS Newsletter

"Over the last 12 months the LWQS and Lake Rotoiti Community Association established a joint working group "FixOhauWall" to represent the Rotorua community and work with the Bay of Plenty Regional Council. Our objectives are to:

  • Have the Regional Council commit to preventing the ongoing leakage of nutrient rich water from Lake Rotorua entering Lake Rotoiti through holes, formed due to corrosion, in the Ōhau Channel Diversion Wall.
  • Re-establish the integrity and functionality of the diversion wall to divert Lake Rotorua water down the Kaituna River, and
  • More actively take steps to improve water quality in Lake Rotoiti and reduce the TLI to its target of 3.5.

The joint FixOhauWall initiative consisted of a media campaign to raise community awareness of the issues of the deteriorating water quality of Lake Rotoiti, the state of the diversion wall and to build community support for action by the Regional Council - with a focus on ensuring that water quality in Lake Rotoiti is improved and that the target TLI for Lake Rotoiti of 3.5, or better, remains the collective goal for the whole community now and into the future. Lake Rotoiti's current TLI is 3.8 and most likely increasing.

Unfortunately, to date, our joint efforts have yet to result in these commitments from the BOP Regional Council nor has the Regional Council provided reassurance that the diversion wall is critical part of the overall Rotorua Lakes restoration programme for the foreseeable future. The current work programme being undertaken by the Regional Council consists of further investigations:

  • An engineering assessment of the condition and ongoing corrosion of the wall.
  • Assessments related to the practicalities for implementing short and long-term solutions.
  • Development of an updated structural report on the wall
  • Assessments of microbial induced corrosion on the king piles (the main structural support members embedded into the Lake Rotoiti lakebed).

The FixOhauWall committee endorses these actions and is looking forward to the outcomes being available early 2026. 

Although these actions are positive steps, The FixOhauWall initiative remains concerned that there has been and remains limited urgency being given to the deterioration of water quality in Lake Rotoiti and the developing constraints this is having on the Lake’s amenity values. The reasons the Regional Council has not taken urgent action to repair the wall are:

  1. Since 2008, the water quality of Lake Rotorua has improved significantly due to alum treatment and catchment land use improvements and that these improvements have reduced and maintained the TLI of Lake Rotorua at or close to 4.2. 
  2. That the wall remains structurally sound and that currently it is considered that the leakage is about 10% through the holes (note this was based on an assessment completed in 2023/early 2024 and corrosion has continued to occur since then).
  3. That cyanobacteria monitoring indicates that the agal assemblages are different between the Ōhau Channel and bays within Lake Rotoiti- therefore the leakage through the wall is not causing water quality decline in Lake Rotoiti.
  4. Repairs to the wall are expensive and that appropriate cost/benefit assessments are required along with consideration of potential alternative solutions including long term improvements to water quality in Lake Rotorua due to the implementation of land change measures.

Over the next few months, the FixOhauWall initiative will be undertaking a work programme to gather more information on the effects of the leaking wall and its potential contribution to the deteriorating water quality in Lake Rotoiti. This includes:

  1. Commissioning Prof David Hamilton to assess the flux of Ōhau Channel water through the wall. This assessment will be based on conductivity changes in Lake Rotoiti relative to Lake Rotorua as L. Rotorua has a higher mineral content due to its geothermal inputs.
  2. Once there is a clearer picture of the flux and its variability, then the impacts of the additional nitrogen and phosphorus entering Lake Rotoiti will be assessed and comparisons made to the original design targets for installing the wall (e.g. the amount of Lake Rotorua nitrogen that needs to be kept out of Lake Rotoiti to maintain and improve its water quality).
  3. Commissioning an independent engineer to review the reports provided by WSP (the Regional Council’s engineering consultant) regarding the corrosion and structural integrity of the both the king and sheet piles of the diversion wall. This review will also consider the adequacy of the methodology used in assessing corrosion and an estimation of the remaining lifetime of the king piles.
  4. We are hosting a special public meeting on Friday 2nd January 2026 at the Lake Rotoiti Sports and Community Centre to inform the community about the Ōhau Wall. Furthermore, we are seeking additional input on what further action the community can take to influence the Regional Council regarding its lack of urgency to repair the wall. All LWQS members are welcome to attend this meeting (see the meeting announcement at the end of this newsletter).

The FixOhauWall committee has also undertaken a fund-raising programme. To date, through the generosity of individuals within the Lake Rotoiti Community we have raised sufficient funds to support our ongoing programme focused on collecting and collating more information to support our case for addressing water quality in Lake Rotoiti and repairs to the Wall. We are grateful for these contributions and are optimistic that they will significantly contribute to speeding up action on preventing the leakage through the wall and improvements to water quality in Lake Rotoiti.

If you would like further information about the Ōhau Channel Wall and the various submissions we have made to the Regional Council, these can be found on the FixOhauWall website. In particular, I recommend you view our submission to the Regional Council on the 7th August as this presents our case for the diversion wall and our concerns about the deteriorating water quality in Lake Rotoiti".

You can read the full LWQS newsletter here.

WE THANK LWQS FOR THEIR AMAZING SUPPORT!