Flood protection and drainage costs may change for many urban and rural properties on the Clutha and Taieri flood and drainage schemes
Learn moreFlood protection and drainage costs may change for many urban and rural properties on the Clutha and Taieri flood and drainage schemes
Tomohaka / Tomahawk Lagoon
Vision: A thriving Tomahawk Lagoon catchment, where water quality and biodiversity are maintained and enhanced through community action, contributing to a healthy ecosystem for all to enjoy.
Tomahawk Lagoon sits at the southern end of the Otago Peninsula and is made up of two shallow brackish lagoons connected by a narrow channel and a weir, with a shared outlet to the sea.
It is a wildlife refuge of 33 hectares managed by the Department of Conservation and home to the threatened plant species Isolepis basilaris. The area is ecologically important as it is defined as a marsh - less than 15% of Otago’s original marshes remain.
The lagoon is a key wetland for waterfowl, waders, and migratory birds, and also provides habitat for native fish and eels.
Citizen Science results indicate that turbidity, E. coli, nitrates and phosphate levels are all exceeding national guidelines. Cyanobacteria, which can be harmful to people and animals, often appears in summer.
In 2017, ORC began working with the local community to address water quality concerns at Tomahawk Lagoon.
ORC committed $260,000 over three years (2022–2025) to support catchment restoration through community-led action. In 2018, two workshops were held with the community to identify community goals and values, and potential projects for the catchment. In 2021, consultation with the community, mana whenua, and key stakeholders helped prioritise actions to be implemented for the catchment.. Initial actions were to set up a permanent water monitoring site and complete an Ecological Assessment.
In 2022, ORC set up a monitoring site at the deepest point of the upper lagoon as part of our State of the Environment programme. You can find the current data on our Environmental Data Portal (named: Tomahawk Lagoon – Tomahawk Mid).
Sampling happens each month, looking at:
Water quality, including:
nutrients
chlorophyll-a
bacteria
clarity
Physical parameters, including:
temperature
pH
dissolved oxygen
conductivity
This compliments the water quality monitoring undertaken by the community, and will show long term trends.
ORC contracted Cawthron Institute to undertake an Ecological Assessment of Tomahawk Lagoon.
The aim of the ecological assessment was to identify drivers for the current ecological status of the lake. As well as to identify possible actions that the ORC, in collaboration with the community, mana whenua, and key stakeholders, could undertake to make the catchment more resilient.
The ecological assessment consisted of an analysis of historical data, and a fieldwork component. The final report on the ecological assessment was submitted to ORC on 31 July 2023, which was then shared to mana whenua, community representatives, and key stakeholders.
Recommended management actions focused on reducing contaminants in the lagoons. These included:
• Exploring the possibility of zoning the catchment as a nutrient-sensitive zone in the Otago Regional Council Land / Water Plan
• Undertaking fencing and riparian planting; buffers in forestry areas
• Enhancing existing wetlands in the catchment
The project was extended for an additional year and received ORC funding from 2022-2026.
As part of the project, ORC worked alongside the community to develop an Implementation Plan to deliver on the recommendations of the Ecological Assessment.
Following the end of the project, landowners and community group from across the upper and lower catchment came together for a day-long tiki tour, visiting four properties to learn about the ORC-funded projects being undertaken, including fencing, planting and weed control.
The day provided an opportunity to build connections, share experiences, and see the catchment through different perspectives. It also highlighted the collective effort and commitment of individual landowners working together to enhance the health of the Tomahawk Lagoon catchment.
Members discussing plant growth (Tomahawk Lagoon landowner get together 16 May 2026).
Discussions outside (Tomahawk Lagoon landowner get together 16 May 2026).
Everyone walking to lagoon (Tomahawk Lagoon landowner get together 16 May 2026).
Community members (Tomahawk Lagoon landowner get together 16 May 2026).
Community members at Tomohaka (Tomahawk Lagoon landowner get together 16 May 2026).
Community members overlooking lagoon from carpark (Tomahawk Lagoon landowner get together 16 May 2026).
ORC partnered with the St Kilda Scout Group to encourage local residents in Tomahawk Lagoon catchment and st Kilda to get involved in the Adopt a Drain initiative and help protect local waterways. To celebrate the group's achievements, a community BBQ and letterbox drop event was held on 14 December 2025.
As part of the project, ORC funding supported the development of a customised "Only Drain Rain" Scout badge, which was awarded to participating scouts (see photo).
In the months leading up to the event, the St Kilda Scouts worked closely with the Catchment Advisor to deliver five stormwater awareness sessions for Keas, Cubs and Scouts. Through a range of hands-on activities, the sessions helped build understanding of how stormwater affects local waterways and what individuals can do to make a difference.
As a result of their involvement, the Scouts adopted two stormwater drains on Victoria Road, adjacent to Tomahawk Lagoon, demonstrating their commitment to protecting the health of the local catchment.
St Kilda Scouts with Janice and the enviroscape (Adopt a Drain at St Kilda Scouts 14 December 2025).
St Kilda Scouts group photo (Adopt a Drain at St Kilda Scouts 14 December 2025).
Tomahawk Stormwater Project Scout badge (Adopt a Drain at St Kilda Scouts 14 December 2025).
Tomahawk Stormwater Project Scout badge design with ORC Logo (Adopt a Drain St Kilda Scouts 14 December 2025).
St Kilda - drain chalking (Adopt a Drain at St Kilda Scouts 14 December 2025).
St Kilda group photo (Adopt a Drain at St Kilda Scouts 14 December 2025).
St Kilda scouts in hi-vis (Adopt a Drain at St Kilda Scouts 14 December 2025).
St Kilda scouts undertaking a letter drop (Adopt a Drain at St Kilda Scouts 14 December 2025).
In response to the community interest for greater awareness of stormwater issues and their impact on local waterways, ORC launched its Adopt a Drain Programme in the Tomohaka/ Tomahawk Lagoon catchment. The initiative encourages local residents to take simple actions to help reduce pollution and protect the health of waterways.
The event brought together community members to hear from Andrew Innes of the ECOTAGO Charitable Trust, who shared the vision for Tomohaka / Tomahawk Lagoon. Attendees also received updates from ORC on project progress and learned about the Adopt a Drain initiative, including simple ways they can get involved and help improve the health of local waterways.
A stormwater education event was held at Domain Hall in April 2024.
Open day held at Tomahawk Lagoon.
If you would like to get involved with the local community on this project, follow them on social media:
If you would like to know more about this project or have any other questions about the work at Tomahawk Lagoon, you can contact our customer services team:
Phone: 0800 474 082
Email: customerservices@orc.govt.nz
