Dune Lakes Project - Q&As

What is the Northland Dune Lakes project?

Dune lakes are precious and rare meaning Northland’s dune lakes are nationally and internationally important. While many of them are in excellent condition, others are slowly degrading and need help.

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.

How will water quality be improved?

The project targets declining water quality. The pressures are many but include stock-access, water runoff with its associated nutrients and sediment, exotic pest fish and invasive water-weeds.

Project work includes removing pest fish, eradicating water-weeds such as Ceratophyllum demersum (hornwort) and Lagarosiphon major (lagarosiphon, South African oxygen weed), educating students and the wider community about threats to dune lakes, fencing out stock, and reducing the impact of drains.

Why are weeds a problem?

Exotic water-weeds are spread accidentally very easily by a range of activities such as boating, duck hunting, eel fishing with nets, digger operations and farm drains. Aquatic weeds can easily outgrow the native plant community, often choking a lake to the point of collapse and resulting in an algal bloom becoming dominant.

This blue-green algae (cyanobacteria) further shades out remaining native plants and depletes oxygen, often killing fish and other aquatic life. A toxic algal bloom can make the water unfit for consumption and/or even skin contact by people or animals.

Aquatic weeds also affect recreational activities such as boating, and swimming. The weeds grow from fragments, so tiny pieces caught on your gear, boats and trailers can be transferred to another unaffected waterbody.

Whilst we plan on eradicating lagarosiphon and hornwort from lakes, we will also be working to stop the spread of weeds and other pests by raising awareness and encouraging people to use the appropriate ‘check, clean, dry’ behaviours before moving between waterways.

Lagarosiphon (Photo Trevor James).Lagarosiphon is one of the exotic water weeds we plan to eradicate from Northland lakes. (Photo credit: Trevor Reed).

How do you plan to remove the weed?

Council has investigated a range of options to remove weeds, including mechanical removal, biological control and treating the lakes with targeted herbicides. Each of these methods has been used in Northland in the past and herbicide has proved to be the most successful long-term option so far.

What restrictions will apply if herbicide is used?

Following application of Aquathol K, there is a water restriction in place for 14 days. NRC have been granted permission from the Environmental Protection Authority (EPA) towards a single, whole-lake application, in order to minimize impact on the community with regards to water take.

What does this mean if I take water from the lake or use it to water my stock?

We will advise stakeholders closer to the operation going ahead in Spring 2020 (estimated to likely happen in early September) to discuss what water restrictions will mean for you because you will need to make alternative arrangements to accommodate the following restrictions after the herbicide application. We also recommend keeping pets/dogs/stock away from the lakes during restrictions. We will be taking periodic water samples to assure you that the herbicide has become undetectable. Although 14 days is the water restriction time specified on NRC’s EPA permission, there is a Tolerable Exposure Limit (TEL) set for this herbicide as it degrades and disappears which we will be monitoring for extra assurance to water users.

Aquathol K (Endothall) Water Restrictions – period after day of herbicide applications
Swimming Fishing for eating or feed Drinking Watering livestock Overhead irrigation
24 hours 3 days 14 days or until residual herbicide is below exposure limits 14 days or until residual herbicide is below exposure limits 14 days or until residual herbicide is below exposure limits

What else are we doing to help our lakes?

  • Pest fish removal for some lakes (including Lakes Ngatu and Waiparera)
  • Fencing and planting. We have provided funding to complete the fencing of Lake Waiparera and the northern side of Lake Wahakari, which will improve the quality of water supply for the Te Kao community, and the full fencing of Lake Shag which sits in the Kai Iwi Lakes group.
  • Over the following two years, the project will also be remedying many drains emptying into the lakes, with sediment traps and riparian planting, including Lakes Ngatu and Waiparera.
  • Education events focusing on water weeds, pest fish and water quality monitoring have been held at four lakes, two of these in partnership with Te Aho Tu Roa, with over 250 students from local schools attending and over 3400 trees planted.

Note: The spelling of Ngakeketo appears on maps as Ngakeketa. Mana whenua iwi advise that this is a misspelling.

Who do I contact if I have any questions or comments?

Please phone council on: (09) 470 1200 or Freephone 0800 002 004
Or email us at: info@nrc.govt.nz