Thousands of birds die at important wetland, from deadly disease caused by pollution

A strange silence has gripped Whangamarino. It is a deathly silence.

The corpses of thousands of dead birds have piled up around the extensive mosaic of swamps, fens, bogs and open water between Waikato's Meremere and Te Kauwhata.

The wetlands are usually an oasis for rare wildlife. It is home to the largest population of matuku (or Australasian bittern) in the world, and its booming calls echo across the water.

But large populations of Whangamarino's birds have fallen sick with avian botulism, dying a gruesome death after losing the ability to walk and use their wings.

The paralysis eventually robs them of the ability to hold up their heads, and they drown in the waters that were once a haven.

Appalled by the outbreak, Fish & Game New Zealand launched a stinging attack on Waikato Regional Council, accusing the local authority of permitting dairy intensification and failing in its statutory obligation to protect freshwater environments.

Fish & Game chief executive Corina Jordan​ said the disease outbreak, in its third month, was "appalling" and a wake-up call for "urgent action".

Devastated Fish & Game staff and community volunteers collected almost 2000 birds, including matuku, in the last month.

Although classed as internationally significant, the wetland had long faced environmental challenges, overloaded with sediment and nutrients from farming and industrial run-off and storm water.

Poor water quality, and changes to how the water flows, had contributed to low oxygen levels in the swamp.

Lake Waikare​, one of the world's most polluted lakes, was diverted into the wetland as part of a flood control scheme.

Locals call it Fanta Lake, because of its vivid orange colour.

As the pools become stagnant, this creates the perfect breeding conditions for bacteria that produces a botulism toxin deadly to birds but harmless to humans.

The toxin is consumed by fish and aquatic invertebrates, which are then eaten by waterfowl.

When Stuff visited the site on Friday, some of the waters were orange and there was an overwhelming, rotting stench.

Jordan said even freshwater eels, which are hardy and able to tolerate low-oxygen environments for short periods, had perished.

"We are concerned at the rhetoric we hear from authorities labelling these incidents as natural," said Jordan, who is a freshwater ecologist.

"Parts of this wetland have been without oxygen for the best part of three months, leading to massive aquatic deaths of even the hardiest freshwater species such as eels. This isn't normal in healthy freshwater wetland systems."

Jordan said the council must now take a "hard look" at how the catchment is managed and limit discharges into the waterways. She also wanted to see a long-term plan for managing Whangamarino.

Ngāti Naho said it wanted "answers not excuses".

"We are tired of the hui with consultants that lack follow-through, or hollow speeches from iwi leaders or mayors that go nowhere," Ngāti Naho Trust​ chief executive Haydn Solomon​ said.

"Our waterways are getting hammered. Our wetlands, lakes, rivers and springs are at breaking point, yet nothing substantive and meaningful is done."

He was cynical about consultation exercises. "Sometimes you are lucky if the local or iwi officials show up to the meeting at all on the waterways.

"But when it comes to the big flash infrastructure projects like the Auckland to Hamilton [transport] corridor, high-density housing, solar farms, expansion of the rubbish dump, or taking more water and sand from our river for Auckland they are all there to clip the ticket.''

Waikato Regional Council science manager Mike Scarsbrook​ said the council is seeking to control intensification of land use and to control the sources of nutrients and sediments into the Waikato and Waipa rivers through a regional plan change.

But it had come up against legal action, with more than 20 appeals.

"Unfortunately, this has been a prolonged process that currently sits under appeal to the Environment Court," he said.

Council lower Waikato zone manager Sarah Lealand​ pointed to work with landowners in the Waikare and Whangamarino catchments to stabilise hill country and stream banks and said flood protection infrastructure was continuously being improved.

"The flood scheme provides an important function in protecting rural and residential properties and key national infrastructure, such as roading, from flooding," she said.

Covering 7290 hectares (about 18,000 acres), Whangamarino is the second largest wetland complex in the North Island.

A draw for duck hunters, it is a roosting and feeding ground for dabbling duck, mallard, grey and shoveler.

It is also the only remaining location for the extremely rare, tiny swamp helmet orchid and a stronghold of the black mudfish.

In 1989 it was listed as a wetland of international importance under the Ramsar Convention, a protection treaty.

Wetlands reduce the impacts of flooding, absorbing heavy rain and releasing water gradually.

They are also a natural buffer for floods and tsunamis, and a recognised tool in climate change mitigation. They are our densest natural carbon store.

But New Zealand has less than 10 percent of its original wetlands left. Between 1996 and 2018, 5761 hectares (14,235 acres) were lost, mainly drained for farming.

Last month, Stuff revealed the government had rowed back wetland protections, introduced in 2020, after pressure from industry groups.

The Department of Conservation (DOC) said it believed at least 1400 birds had been affected, but has had no reports of dead or sick matuku, or mudfish, but confirmed eels had died.

DOC Hauraki, Waikato and Taranaki director of operations Tinaka Mearns​ said the outbreak was concentrated on the Whangamarino and Maramarua rivers.

"Historically there has been a matrix of management models and organisations that need to work together to manage wetlands like Whangamarino and other waterways across the country," she said.

"New Zealand as a whole is getting to grips with this legacy and DOC is working constructively with other agencies, tangata whenua, land-owners and other stakeholders to address these issues. We are optimistic and motivated to work with others to improve our wetlands."

* This story originally appeared onStuff.