How we’re protecting Auckland’s water supply during council pest control operation

Update 29 October 2025

Wairoa and Upper Mangatawhiri dams out of service during Auckland Council’s second pest control application

Our Wairoa and Upper Mangatawhiri dams have been taken out of service today ahead of Auckland Council’s pest control operation in the Hūnua Ranges. Once the 1080 drop is complete, a stringent water quality testing regime will be carried out over several days. The dams will only be returned to service when consecutive samples at multiple locations within each dam confirm no trace of 1080 is detected in the water.

Our water quality monitoring plan has been reviewed by the Ministry of Health as part of the council's permit application for the use of 1080 across the Hūnua Ranges.

Testing will be carried out by Watercare Laboratory Services, an IANZ accredited lab with IANZ-approved test methodology for 1080.

This information below will be updated as results come in:

Wairoa Dam water testing results:

• 4-8 hours after drop: 1080 undetected at all sampling locations

• 20-24 hours after drop: 1080 undetected at all sampling locations

• 40-48 hours after drop: 1080 undetected at all sampling locations

Upper Mangatawhiri Dam water testing results:

• 4-8 hours after drop: 1080 undetected at all sampling locations

• 20-24 hours after drop: 1080 undetected at all sampling locations

• 40-48 hours after drop: 1080 undetected at all sampling locations

Update: 28 October 2025

The rainfall late last week triggered further sampling of the water in Cosseys and Mangatangi dams. All of these samples showed no 1080 detected in the water.

Update: 20 October 2025

As all water samples showed no 1080 detected in the water, we are returning Cosseys and Mangatangi dams to service. Sampling from the valve towers, and at the Ardmore Water Treatment Plant, will continue for four weeks.

Update: 17 October 2025

Cosseys and Mangatangi dams out of service during Auckland Council’s first pest control application

Our Cosseys and Mangatangi dams have been taken out of service ahead of Auckland Council’s pest control operation in the Hūnua Ranges. Once the 1080 drop is complete, a stringent water quality testing regime will be carried out over several days. The dams will only be returned to service when consecutive samples at multiple locations within each dam confirm no trace of 1080 is detected in the water.

Our water quality monitoring plan has been reviewed by the Ministry of Health as part of the council's permit application for the use of 1080 across the Hūnua Ranges.

Testing will be carried out by Watercare Laboratory Services, an IANZ accredited lab with IANZ-approved test methodology for 1080.

This information below will be updated as results come in:

Cosseys Dam water testing results:

• 4-8 hours after drop: 1080 undetected at all sampling locations

• 20-24 hours after drop: 1080 undetected at all sampling locations

• 40-48 hours after drop: 1080 undetected at all sampling locations

Mangatangi Dam water testing results:

• 4-8 hours after drop: 1080 undetected at all sampling locations

• 20-24 hours after drop: 1080 undetected at all sampling locations

• 40-48 hours after drop: 1080 undetected at all sampling locations

Update: 13 August 2025

Auckland Council begins its latest predator control operation in the Te Ngāherehere o Kohukohunui/Hūnua Ranges Regional Park tomorrow.

The operation will cover the Te Ngāherehere o Kohukohunui/Hūnua Ranges parkland, neighbouring Department of Conservation (DOC) administered land reserves, and some private land.

The operational team will carry out the first stage of the project, laying pre-feed, on Thursday August 14 and Friday 15 August. The park will be closed to the public from Wednesday evening (August 13) until midday Friday (August 15).

The council’s 1080 aerial pest control operations in the Hūnua Ranges are undertaken in winter, when pests are most likely to be hungry, visitor numbers are at their lowest and ahead of the key breeding time for several of our native bird species.

The pre-feed phase of the operation familiarises pest animals with the cereal baits, ahead of the baits containing 1080 (sodium fluoroacetate) being applied in the following weeks.

A satellite navigation system (GPS) and custom-designed bait applicators will be used to distribute bait by helicopter across the operational area.

Protecting Auckland’s water supply

Watercare headworks manager James Talbot will ensure the dams are out of service ahead of the operation and they will only be returned to service after a stringent water quality testing regime confirms there is no trace of 1080 in the water.

"Our dams in the Hūnua Ranges are Auckland’s most important water sources, normally supplying about two thirds of Auckland’s water.

"As we’ve done for previous 1080 operations, we’ll be taking every precaution to protect the water stored in these dams.

"Auckland Council will ensure helicopters carrying bait will not fly over the reservoirs, and there will be setbacks from the margins of each reservoir. While the bait application is being carried out, the dams will be out of service and they will only return to service once a comprehensive water sampling programme has been completed confirming the water is safe for supply.”

This page will be updated with sampling results for each dam as they come in.

More about the council’s pest-control operation

The operation is part of a long-term conservation strategy to protect endangered species such as kōkako and preserve the ecological integrity of one of the region’s largest remaining tracts of native forest.

The aerial operation of non-toxic pre-feed bait will be spread across the roughly 23,500-hectare operational area. This will be followed by the application of baits containing 1080 (sodium fluoroacetate) a proven method of controlling possums, rats and stoats across large, forested areas. The operation aims to reduce populations of introduced predators that threaten native birds, plants, and ecosystems.

To manage the large area and protect water-supply reservoirs, the operational areas will be divided into two blocks:

• Cosseys and Mangatangi

• Wairoa and Mangatāwhiri.

For more information about council’s pest control operation, click here.