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Tomohaka / Tomahawk Lagoon
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In 2017, in response to concerns about water quality, our staff began to work with the local community to scope lake restoration works for Tomahawk Lagoon.
Water quality was found to be degrading with elevated levels of sediment, E. coli, nitrates and phosphates found within the lagoon and Lagoon Creek (a contributing waterway).
Cyanobacteria (toxic algae) is found within the lagoon regularly in the summer months. The community also raised other concerns to do with water levels and sediment.
With the establishment of the Environmental Implementation Team in 2021, together with mana whenua, stakeholders, and the community we agreed on 3 key goals: an ecological assessment of the catchment, the support and formation of a catchment group and the establishment of a permanent water quality monitoring site for the lagoon.
Tomahawk Lagoon is located at the southern end of the Otago Peninsula. It consists of two shallow brackish water lagoons which are joined by a narrow channel and weir/gate structure and share a common sea outlet.
Tomahawk Lagoon is a wildlife refuge of 33 hectares that is managed by the Department of Conservation which contains the threatened plant species Isolepis basilaris on the margin of the lagoon. The area is important ecologically as it is defined as a marsh and less than 15% of original marshes remain in Otago.
The lagoon is a regionally significant wetland habitat for waterfowl and waders with a variety of bird species present and is part of a chain of feeding habitats along the coast used by migrating birds. Tomahawk Lagoon is also important habitat for native fish and eels.
Citizen Science water quality monitoring is undertaken by ECOTAGO monthly. ECOTAGO are a community group who are working to test and improve water quality within the Tomahawk Lagoon catchment.
Their results indicate that turbidity, E. coli, nitrates and phosphate levels are all exceeding national guidelines. Cyanobacteria is also regularly found within the lagoon over the summer months which is a toxic bacterium which can be harmful to humans and animals.
with gee minnow nets at Tomahawk Lagoon
ORC has dedicated $260,000 over three years (2022-2025) to enhance the Tomahawk Lagoon Catchment through community action to contribute to a healthy ecosystem for all to enjoy.
In 2018, two workshops were held with the community which identified community goals and values for the Tomahawk Lagoon catchment, and it identified potential projects for the catchment.
In 2021, a consultation process was undertaken with the community, mana whenua, and key stakeholders to vote on the highest priority actions to be implemented for the catchment.
The three priority actions that were identified by the community, mana whenua and key stakeholders in 2021 were:
- Catchment group formed and supported
- Joining of agencies and the community. Establish a ‘Friends of Tomahawk Lagoon’ with members of the community and stakeholder representatives
- Water Quality data
- Have a permanent water quality monitoring site installed to establish baseline data and ensure mahika kai safety.
- Ecological Assessment
- Investigate the balance between the needs of human interaction with the lagoon and wildlife (hydrological function, ecology, wildlife, walking tracks, flood hazard, core sample). Include assessment of what the limits are for the system in this catchment (tipping point). What are the key stressors and how resilient is the catchment. What actions do we need to undertake to make the catchment more resilient.
The three priority actions, along with the collective vision and values for Tomahawk Lagoon, were compiled in the Tomahawk Lagoon Outline Management Plan.
This outline management plan was then approved by council for delivery.
ORC has been supporting the community and the Otago Catchment Community Inc in the formation of the Tomahawk Lagoon catchment group. Steve, Dean and Andrew from Tomahawk lagoon citizens science team have been working hard to develop this group and encourage other community members to join.
This work is being led by the community and Otago Catchment Community. ORC continues to support community members in the formation of a ‘Tomahawk Lagoon Catchment Group’.
ORC contracted Cawthron Institute to undertake an Ecological Assessment of Tomahawk Lagoon. 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 and 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 focussed 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
ORC has established a monitoring site as part of our State of the Environment programme (August 2022) in the deepest point of the upper lagoon. The site name is Tomahawk Lagoon at Tomahawk Mid, and we perform monthly sampling for various water quality parameters (e.g., nutrients, chlorophyl-a, bacteria levels, and water clarity) and physico-chemical parameters (water temperature, pH, dissolved oxygen, conductivity, etc).
A stormwater education event was held at Domain Hall in April 2024.
Open day held at Tomahawk Lagoon.
Associate Professor Marc Schallenberg demonstrating the scientific value of sediment core samples at an Open Day event at Tomohaka / Tomahawk Lagoon.
local school pupils getting involved in the science at Tomahawk Lagoon.
local school pupils getting involved in the science at Tomahawk Lagoon.
ORC has developed an Implementation Plan with the community.
The Vision is a thriving Tomahawk Lagoon catchment, where water quality and biodiversity are maintained and enhanced through community action to contribute to a healthy ecosystem for all to enjoy.
ORC has more funding available to help landowners enhance habitat on their properties, particularly wetlands and alongside creeks.
More stormwater education and signage is being developed.
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
