After years of discussion, research and planning, work to solve engineering and environmental challenges at Tomohaka/Tomahawk Lagoon still seem to be in the distant future.
Tomahawk Lagoon sits on the ocean side of the Otago Peninsula, behind Tomahawk and Smaills Beaches.
Split into upper and lower basins, the lagoon is a wildlife refuge for waterfowl and waders, including species such as white heron (kōtuku).
There have been several flooding incidents at the lagoon. A weir designed to release water from the upper to the lower basin has not been working properly, meaning upper-basin levels can contribute to flooding.
The lower basin has an outlet to the sea, but sand build-up can block it, causing flooding in the lower lagoon and trapping saltwater and seaweed that cannot flush out, reducing water quality.
The water quality has been monitored by citizen-science group Ecotago.
In its 2021-31 long-term plan, the Otago Regional Council set aside $260,000 — $100,000 in 2021-22 and $80,000 in both 2022-23 and 2023-24 — for Tomahawk Lagoon projects, including an ecological assessment.
This assessment of the lagoon was completed in 2023 and an implementation plan was developed.
The regional council told the Otago Peninsula Community Board at its latest meeting it had pulled back from engineering work and was signalling new studies, without firm funding plans or a timetable.
Otago Peninsula Community Board chairman Paul Pope said the regional council appeared to be doubling up on research already done.
"It’s like, hang on, doesn’t that look like the same thing you’ve done only two years ago?"
The lagoon, its water quality, biodiversity, sand and beach formed a single catchment that needed co-ordinated management, Mr Pope said.
"The positive is we have finally got a relationship with the regional council and we have finally got them to start understanding and appreciating what needs to be done to protect the community and the lagoon.
"The kind of concern I've got is we don't need them to rebuild the wheel, recreate the wheel."
Mr Pope wants the regional council to anchor next steps in completed work, including the ecological assessment and the implementation plan and to set dated milestones for hydrological modelling that will guide decisions on the weir and the ocean outlet.
The community needed regular updates, ideally quarterly, to ensure it was able to understand what progress was being made over time.
The regional council has undertaken work to remove sand to allow the lower lagoon to drain, helped by locals who alert staff when sand build-up return.
"The community's quite motivated around this area, and they live here because it's a lagoon and they love it."
There had to be a balance between human health and wellbeing as well as biodiversity, such as managing flood risks.
"You don't want to live here and go, this is lovely, and then wake up and realise instead of putting your slippers on, you're putting your boots on."
Otago Regional Council manager environmental implementation, Libby Caldwell said rather than creating a single master plan for Tomahawk Lagoon, the goal was to ensure all current and future work was well-informed, thoroughly aligned across council departments and based on robust engineering, environmental and cultural understanding.
"This approach respects historical issues and opportunities, ensuring they are clearly identified and addressed."
Under the regional council’s 2021-31 long-term plan funding, the council worked collaboratively with partners and key stakeholders to finish an implementation plan based on the 2023 ecological assessment.
The vision was a thriving Tomahawk Lagoon catchment, where water quality and biodiversity were enhanced through community action to contribute to a healthy ecosystem for all to enjoy.
Activities have focused on reducing contaminants entering the lagoons, enhancing habitat, and supporting community education.
An investment of $176,436 has been made to habitat enhancement through funding agreements with the community sharing costs and labour with the regional council 50-50.
The community will install 3.3km of fencing, plant at least 9846 native plants and remove plant pests from 2.4ha.
Fifteen sites throughout the catchment will be enhanced, covering 18.9ha.
Education initiatives received $38,333 of funding which supported Ecotago and facilitated a community stormwater event; $16,680 of fund remains in the 2025-26 financial year.
It is intended this remaining budget would be spent on exploring the installation of sediment traps in the catchment and installation of signage to communicate the value of the area.
"The long-term outcomes of the implementation plan are to improve stream and lagoon water quality, and to enhance native aquatic and terrestrial biodiversity."
Work so far has focused on the high priority management actions outlined in the 2023 ecological assessment.
The ecological assessment that has been undertaken will be able to inform the regional council’s future work programmes in the catchment by addressing existing gaps and providing essential evidence for future consents and delivery of work.
Hydrological modelling work is proposed to be conducted in-house to reduce costs and leverage the regional council’s internal expertise.
"This approach ensures decisions on the weir and outlet are grounded in a comprehensive flood risk assessment," Mrs Caldwell said.
