About the dune lakes project

The goal of the project is to improve the water quality of a number of Northland’s dune lakes through a range of work streams that specifically target the threats to dune lakes.

Over the five-year project, we will be:

• Eradicating water-weeds
• Controlling pest fish
• Removing grass carp
• Stock exclusion through fencing and reticulation
• Remedying nutrient and sediment inputs
• Education about dune lakes for school students and local communities
• Collaborating with tangata whenua and other key partners

Freshwater Improvement Fund

The Ministry for the Environment’s Freshwater Improvement Fund (FIF) commits $100 million over 10 years to improve the management of New Zealand’s lakes, rivers, streams, groundwater and wetlands. As part of the FIF, the Northland Regional Council received matching-funding to improve the water quality of some of Northland’s dune lakes. The total project value is $1,565,950 over five years.

The council has a second FIF project - Waimā Waitai Waiora - aimed at improving water quality in the Northern Wairoa River and its tributaries.

Eradicating water-weeds

The focus of this workstream is the eradication of the invasive water weed Lagarosiphon major  from Lake Ngatu and Ceratophyllum demersum  (hornwort) from five other lakes.

In the past, a range of options were used to remove weeds, including mechanical removal, biological control (grass carp) and treating the lakes with targeted herbicides. Each of these methods were used in Northland in the past. The herbicide has proved to be the most successful long-term option so far. Endothall targets the invasive aquatic weeds Lagarosiphon major and Ceratophyllum demersum (hornwort) and doesn’t affect native plants or fish. Microbes in the lake bed break it down into its constituent elements: oxygen, carbon, hydrogen, and potassium. In the spring of 2020, council used Endothall (Aquathol K) to successfully control Lagarosiphon major  in Lake Ngatu. In the summer of 2022, council used Endothall (Aquathol K) to successfully control hornwort in Lakes Tutaki, Egg and two lakes at Mt Camel.

Controlling pest fish

The workstream is focused on the removal of several species of pest fish from eight lakes. The aim of the project is to:

• control pest fish in high priority lakes through manual netting, trapping and electrofishing
• facilitate communities and landowners to continue pest fishing under NRC’s permits

As part of the Freshwater Improvement Fund (FIF) Dune Lakes project, a mail survey was conducted to obtain information on the distribution of four invasive water weeds and exotic fish. The results from this survey have helped the project team to prioritise pest fish control operations.

Removing grass carp

This workstream is focused on removing grass carp from four dune lakes: Roto-otuauru (Swan), Midgley, Waingata and Heather. Herbivorous grass carp were introduced to these lakes to eradicate and prevent the spread of highly invasive oxygen weeds such as hornwort and egeria. This will also help prevent their spread to other high-value dune lakes. The fish must now be removed to allow the lakes to return to a vegetated state.

Stock exclusion through fencing and reticulation

This workstream included fencing out stock at several key lakes with some reticulation where required. These lakes included Shag (just north of the Kai Iwi Lakes), Midgley’s (west coast), and Wahakari (Far North).

Remedying nutrient and sediment inputs

This workstream seeks to manage the amount of nutrients and sediment entering select dune lakes through remedial work on drains and gullies and redirection of flows, by constructing swales, sediment traps and wetland areas. Swales and sediment traps were constructed at Lake Ngatu and a wetland area planted by the local school on the lake edge. More work is planned near Black Lake, one of the Kai Iwi Lakes. 

Education, information and community support

This workstream includes a series of ‘get to know your dune lake’ field days for students from local schools and their communities. These field days include hands-on learning sessions looking at lake plants, fish and learning about water quality. Education events have been held at ten lakes, including Lake Ngatu (Awanui), Lake Waiporohita (Karikari) Lakes Kanono and Humuhumu (Poutō) and the Kai Iwi Lakes. These events have been run in partnership with the Enviroschools and Te Aho Tu Roa programmes, and over 600 students have attended so far. Another six events are planned for the coming year.

A collaborative project

The project works in partnership with mana whenua iwi and hapu to ensure the cultural values and aspirations of mana whenua are considered and included in the planning and delivery of the project.

Community engagement is also key to the success of the project and a number of events are planned to ensure local residents and landowners are informed and have the opportunity to provide feedback and have any queries or concerns addressed.

We are also working with a range of partners to protect and restore some of Northland’s dune lakes:

• Ministry for the Environment
• Ngāti Kurī
• Te Aupōuri
• Ngāi Takoto
• Te Rarawa
• Te Roroa
• Te Uri o Hau
• Patuharakeke
• Ngati Whatua
• Enviroschools
• Te Aho Tu Roa
• Department of Conservation
• Northland Fish & Game Council
• Far North District Council
• Kaipara District Council
• NorthTec

Get in touch

For more information on the project, you can contact the team by email at: [email protected]

Further information