Whangamarino Wetland in decline with fire, pollution and bird loss

Tuesday, 24 February 2026

Whangamarino Wetland has been burning, flooding and choking.

The north Waikato wetland, near Te Kauwhata, was once described as a national stronghold for matuku (Australasian bittern). Now, after decades of pressure and two back-to-back disasters, a new report says its ecological character has declined — and in some cases, beyond acceptable limits.

The message from the Department of Conservation report is blunt: the internationally recognised wetland’s decline is measurable.

“Active intervention is critical,” the report says - though those involved note the degradation took a long time, and so will a turnaround.

Waikato Regional Council is leading development of an action plan for the 7000-hectare site, which spans swamps, fens and peat bogs.

The wetland is one of seven NZ wetlands listed under the Ramsar Convention. However, it’s gone downhill ecologically since it was listed in 1989, according to the DOC report released on Tuesday.

Of 18 indicators assessed, 12 show either an actual or likely decline. Four are confirmed as being beyond the limit of what’s acceptable: nitrogen levels in the water, habitat loss from fire, the population of matuku, and ecosystem services recognised by mana whenua.

Water quality is a major concern. Total nitrogen levels have more than doubled since designation, rising from about 1.4 mg/L to 2.6 mg/L. The report states the recommended nitrogen limit for the wetland is 0.8 mg/L.

That decline was thrown into sharp relief over summer 2022–23, when a “blackwater event” led to very low oxygen levels and an avian botulism outbreak. More than 1500 dead birds were collected, alongside dead fish. DOC says poor water quality, floods and the input of contaminants and organic matter triggered the event.

“Whangamarino has faced mounting pressures for decades, but recent events have made things worse,” regional director Tinaka Mearns said.

Just over a year later, in October 2024, a human-induced fire burnt 1039 hectares of raised bog. More than 15% of the Ramsar site was affected, with “almost complete loss of above ground vegetation” in the burn area.

Birdlife has also suffered. The report confirms an actual decline in matuku numbers, with monitoring showing near record low levels between 2019 and 2022. No current numbers were provided but a 1981 survey recorded 145 bittern, and the population is now described as under critical threat.

For Waikato Tainui, the wetland’s decline is not only ecological but cultural. The report states mana whenua report a significant and ongoing loss of ecosystem services since 1989.

Restoration must address the whole system, Waikato Tainui oranga general manager Marae Tukere said - “water quality, hydrology, invasive species, and land use, not just individual symptoms”.

The report notes complex drivers of the wetland’s woes: water level and flow, nutrient loading, invasive species such as koi carp, and fire. While minimum water levels have been restored since the early 2000s, flood frequency and sediment inputs are still a concern.

It recommends reviewing catchment management to improve water quality, better protecting the wetland from fire, improving water level management, and increasing control of pest plants and animals.

Waikato Regional Council will lead the development of an action plan for Whangamarino, supported by DOC, Waikato Tainui, Waikato River Authority, mana whenua representatives, Fish and Game, landowners and other stakeholders.

The plan will also look at the nearby Lake Waikare, which feeds into the wetland.

The report was produced to meet New Zealand’s obligations under the Ramsar Convention on Wetlands - it must notify the Convention if the ecological character of a Ramsar wetlands has changed or is likely to.