Ōtuwharekai is a nationally important inter-montane wetland, lake and braided river site that has outstanding biodiversity values and high cultural significance to Ngāi Tahu.

Conservation efforts in Ōtuwharekai are focused on protecting braided river birds through predator control, restoring ecosystems by large-scale weed control, improving water quality of the Ashburton lakes and streams, and monitoring the status of threatened plant and animal species that rely on the site. We also support community trapping initiatives to protect wetland birds from predators.

Key projects

Braided river bird recovery

AK objective: Enhance species diversity and protect threatened species
Site target: Increasing nesting success of wrybill and other threatened braided river birds

The rare and dynamic braided river environment provides habitat for a range of threatened bird species like wrybill, kakī/black stilt and black-fronted tern. Protecting these birds and enhancing their habitat through advocacy and weed and predator control is a key part of our conservation efforts.

We’re reducing nest predation rates through predator control - black-fronted tern nest predation drops to 38%, compared to 96% outside the control area.

Our monitoring programme has shown that nationally critical kakī are nesting in the Upper Rangitata River, and we have successfully banded kakī chicks

Ashburton Lakes ecosystem health

AK objective: Maintain or enhance water regime and water quality
Site target: Tropic status (TLI) of Lake Heron is <2 TLI; and for (all other Ashburton lakes is <3 TLI

Water quality and ecosystem health vary between the lakes – some are close to pristine, while others are in poor condition. Our research has focused on monitoring water quality and native aquatic plant communities. Aquatic plants provide habitat for aquatic life, regulate water quality by absorbing nutrients and binding sediment, and are a useful indicator of lake health.

We are working with Environment Canterbury, iwi and landowners to improve management regimes and reduce sediment and nutrient loads entering the lakes.

Threatened plant recovery (Craspedia)

AK objective: Enhance species diversity and protect threatened species
Site target: Increasing population of Craspedia heron

The critically endangered Craspedia (heron) only grows near Lake Heron. To ensure the survival of this incredibly rare plant species we are monitoring the existing population on Cameron Fan, as well as collecting seed so the DOC nursery can store and grow plants which can then be translocated to Lake Heron. Trial plantings at different sites around the lake are underway.  

Weed control

AK objective: Enhance species diversity and protect threatened species.
Site target: Grey willow, crack willow, broom and lupin are managed at low levels.

Invasive plant species put pressure on threatened native plants and ecosystems. We are using aerial and ground control methods to manage woody and ground-cover weeds across 12,000 ha of wetlands, riparian habitats and the Upper Rangitata River. Removing weeds will enable recovery of native vegetation and enhance landscape values.

Kettlehole wetland protection

AK objective: Protect or restore ecosystem condition
Site target: All kettleholes on conservation land are protected and retain high plant diversity dominated by native vegetation

Seasonally wet kettleholes support rare ephemeral turf vegetation. To protect these native turf communities and other threatened plant species we are controlling rabbit populations to a low level and managing weeds around the kettleholes.

Skink monitoring

AK objective: Enhance species diversity and protect threatened species
Site target: A long-term conservation plan for threatened skinks is prepared by 2020

A 10-year study on the Nationally Vulnerable scree skink was completed in 2018 which identified population trends, habitat range and threats, and showed that the skinks are highly vulnerable to mammalian predators and flood events. Based on this knowledge we aim to develop and implement a plan for securing scree skink populations. 

Kākahi (freshwater mussel) populations

AK objective: Enhance species diversity and protect threatened species.
Site target: Safeguard kākahi populations in the Ōtuwharekai basin

A survey carried out by NIWA in February 2021 assessed the state of kākahi populations in eight of the Ōtuwharekai lakes, comparing this to results from a previous survey in 2012. DOC is involved in a collaborative process – with all basin landowners, Ngāi Tahu, Te Rūnanga o Arowhenua, Te Ngāi Tūāhuriri Rūnanga and Te Taumutu Rūnanga, Environment Canterbury, Land Information New Zealand, Ashburton District Council, and Fish & Game – and commissioned the survey as part of ongoing efforts to prevent further degradation of lake and stream ecological integrity in the basin.
The surveys recorded kākahi in all eight lakes, with the overall distribution, their density, and population size structure having increased or remained similar for most lakes compared with the last survey (2012 to 2021).  However, there was a concerning decrease in the density of kākahi aggregations in Lake Emily (c. 60 % decline) and Māori Lake West (17 % decline).  Poor shell condition was also noted for individuals in Lake Clearwater.  Similar to 2012, there was a concerning absence of smaller kākahi in the lakes, which likely indicates that recruitment has been impacted for many years.
DOC would like to thank all those who helped out during the week, and the landowners for allowing access to undertake the surveys.

Report cards

• Ōtuwharekai – habitat 2015 (PDF, 3,181K)
• Ōtuwharekai – habitat 2016 (PDF, 6,831K)
• Ōtuwharekai – scree skink 2015 (PDF, 2,414K)
• Ōtuwharekai – weed control 2016 (PDF, 6,994K)
• Ōtuwharekai – wetland 2015 (PDF, 2,073K)

Science publications

• Cultural Health Assessment of Ōtuwharekai / The Ashburton Lakes on the Takiwā website
• Impacts of deforestation on the ScienceMag website
• Nutrient load balance for Lake Clearwater on the Informit website
• Water quality of Ōtuwharekai – Ashburton lakes and streams: LakeSPI report (PDF, 2,483K)
• Ecology of scree skink on New Zealand Ecology website
• Repeat survey of kākahi (freshwater mussel) in the Ōtuwharekai Lakes (PDF 2,757K)

See all our publications in the Arawai Kākāriki science bibliography.

Key partners

Working in partnership with organisations and communities to share knowledge is an intrinsic element of Arawai Kākāriki.

Key partners involved with Ōtuwharekai:

• Te Rūnanga o Arowhenua
• Environment Canterbury
• Fish and Game New Zealand
• Ashburton District Council
• Forest and Bird
• Rangitata Landcare Group
• Land Information New Zealand
• LEARNZ
• Cawthron Institute
• Lake Clearwater bach owners
• Landowners
• Recreational groups

Get involved

Volunteer groups involved in Ōtuwharekai:

• Forest and Bird – Ashburton Branch (weed control, annual winter bird counts)
• Māori Lakes volunteer trapping group (predator control)
• Lake Heron volunteer trapping group (predator control)
• Lake Clearwater Hut Holders Association

Find other DOC volunteering activities. 

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