The Wall
History of the wall
Designed to protect the water quality of Lake Rotoiti, the 1,275-metre-long wall redirects nutrient-rich water flowing from Lake Rotorua via the Ōhau Channel, sending it directly down the Kaituna River.
The Ōhau Diversion Wall was completed in July 2008 as a critical intervention within the $200 million Rotorua Lakes Protection and Restoration Programme. This sheet pile wall is anchored with king piles extending up to 70 metres into the lakebed and was constructed with a low visual profile extending 500mm above the waterline.
The Ōhau Diversion Wall was built at a cost of just below $9 million, paying another $1 million for design and consenting; thus, the total project cost was around $10 million. The funding for this undertaking came mainly from the Bay of Plenty Regional Council, with the New Zealand Government providing a grant of $4 million to cover the investment partly. The wall is the primary Lake Rotoiti intervention, alongside sewage reticulation and stream and lake margin plantings.
Since its implementation, the wall has had a transformative impact. It was predicted to reduce algal bloom risk by 40% and, for over a decade, delivered visible improvements to Lake Rotoiti’s water clarity and ecological health. Water quality monitoring and scientific modelling consistently showed that the wall diverted up to 99.3% of the Ōhau Channel’s inflow away from Lake Rotoiti.
The Ōhau Wall
The wall is no longer doing its job. The onset of corrosion was revealed in 2014, and in 2019, it was observed that the wall had developed many holes, some of which are easily recognisable from the lake surface.
Six years later, in 2025, with little to no intervention, the breaches reversed any environmental gains made and violated the conditions stated in the resource consent regarding the maintenance of the wall.
Flow monitoring in 2024 highlighted negative velocities along several parts of the wall, indicative of bidirectional flow clearly violating its intended function.
Urgent repairs are no longer optional. Through various technical reports, the experts conclude that the wall segments, which are in a terrible condition, need to be reinforced structurally or replaced.
Our preferred solution is the durable circular PVC modules, which make the wall impermeable again and thus extend its life and purpose for up to 100 years with only limited future inspections needed.
It is clear that the longer we wait, the more serious the risk of ecological degradation to a national treasure will be. On the other hand, the public will trust the regional council less and less regarding environmental stewardship.
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Important articles & Documents
Explore articles and documents illustrating the truth and the crisis resulting from the Ōhau Diversion Wall’s degradation. The materials outline the technological, ecological, and social aspects that require intervention now.
LWQS - Presentation-BoPRC Ohau Channel Wall - December
File Size: 8.18MB
David Hamilton 2009
File Size: 887KB
Ohau Wall Water Quality Annual Monitoring Report 2018 - 24
File Size: 3.97MB
RM16-0527 Consent Conditions FINAL
File Size: 468KB
Ohau Diversion Wall 7 year Review - Report
File Size: 2.48MB
1-C1403 Ohau Diversion Wall Detailed Analysis Report
File Size: 2.24MB