Dramatic new maps have revealed the enormous loss of our natural wetlands - and undoing the damage will take years, Conservation Minister Eugenie Sage says.

Around 90 per cent of these soggy refuges - vital for supporting plant and animal life - have vanished in the face of development.

Home to an abundance of species like shorebirds, eels, whitebait, mangroves and kahikatea, our wetlands once stretched across 2.2m ha of countryside - that had now dwindled to 249,776ha.

Southland lost 1000ha in just the last decade.

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Sage described wetlands as kidneys that captured sediments and nutrients, and slowly released water in drought-prone areas.

"They are home to precious wildlife and plants and are wonderful places for people to experience nature," she said.

"We must protect the last 10 per cent."

But it would take a "concerted and serious effort" - and years - before the trend could be turned around.

Rare and threatened species that relied on our remaining wetlands include the Australasian bittern or matuku, and the Canterbury mudfish.

The Corybas carsei, or swamp helmet orchid, now only had one population remaining, at the Whangamarino Wetlands near Te Kauwhata in northern Waikato.

There had been good work by authorities, community and environment groups, iwi, companies and land owners, Sage said, but much more effort was needed.

She wanted to see more sites protected under the Ramsar Convention on Wetlands of International Importance.

New Zealand only had six among nearly 2300 worldwide - and the Department of Conservation was now looking at options.

"There needs to be more replanting of wetlands and better use of the Resource Management Act to ensure they are considered when intensive developments and agricultural expansions are being considered," she said.

A pukeko takes flight within the Whangamarino Wetlands, in Waikato. Photo / File
A pukeko takes flight within the Whangamarino Wetlands, in Waikato. Photo / File

"These unique areas are too important for New Zealand's native wildlife and plants to lose.

"The Government will do more and continue to [offer] support for communities working hard to achieve long-term wetland conservation."

Forest and Bird's freshwater advocate Annabeth Cohen said our original wetlands had been "destroyed" by agricultural and urban development - and we weren't doing a good job of protecting what was left.

A fifth of native bird species used wetlands as their primary habitat, relying on a linked series of wetlands for resting and feeding.

"The trouble is, our original wetlands have been drained for agriculture, and the now rare remnants can't cope with the huge amounts of nutrient and sediment-loaded runoff, which degrades the quality of the water, making it very difficult for whitebait, eels, and other native freshwater species to survive there," Cohen said.

Auckland's wetlands extent before human occupation. Image / Forest and Bird
Auckland's wetlands extent before human occupation. Image / Forest and Bird

"Wetlands can occur in many places, from estuaries to mountain-tops, but very few of these special ecosystems remain.

"Those that do remain are often isolated and don't provide the connection that wildlife need."

To mark World Wetlands Day, Forest & Bird has released maps that showed the extent of wetland loss, comparing the situation before human settlement, with few remnants.

Of all regions, Nelson had by far lost the greatest proportion - 99.2 per cent - while Waikato had lost the largest area: a total 328,290ha.

Waiatarua Reserve wetlands, in Remuera. Freshwater wetlands once comprised about 25 per cent of the region's land cover, but they now comprise less than 0.5 per cent. Photo / File
Waiatarua Reserve wetlands, in Remuera. Freshwater wetlands once comprised about 25 per cent of the region's land cover, but they now comprise less than 0.5 per cent. Photo / File

The Auckland region once had some 57,851ha of wetland ecosystem, of which just 2639ha, or 5 per cent, remained.

The low-lying western suburbs of the city were once full of cabbage trees and flax, and formed habitat for weka, banded rail, bittern and pukeko.

On the Auckland isthmus, swamps developed behind beach deposits at the mouths of streams, along streams restricted by lava flows, in ponds in volcanic craters and on the surface of lava flows.

Swamp forests with kahikatea, pukatea, swamp maire, raupo, cabbage trees and harakeke would have once covered large expanses of the low lying areas of the Kaipara and Franklin districts and also parts of Rodney.

Pekapeka Wetlands, south of Hastings. Before human occupation, the Hawke's Bay region had 113,362ha of wetland ecosystem - only 2458ha is left. Photo / File
Pekapeka Wetlands, south of Hastings. Before human occupation, the Hawke's Bay region had 113,362ha of wetland ecosystem - only 2458ha is left. Photo / File

Te Henga was the largest remaining wetland in Auckland and home to a wide range of native animals including bittern, fern bird and spotless crake and pateke, or brown teal.

In Wellington, only 2 per cent of 122,804ha was left.

The Hutt Valley was once marshlands and swamp forest, which was dominated by raupo, flax and toetoe, and extended several kilometres up the valley from the river mouth at the time of European arrival.

Kahikatea, matai, puketea and rimu forest grew extensively on the valley floor, which had since been mostly cleared.

Significant remaining wetlands in the Wellington region included Pencarrow lakes, the Waikanae estuary and the Pauatahanui inlet.

In Canterbury, where 187,115ha of cover had dwindled to 19,851ha, was the most important wetland of its type, at Lake Ellesmere.

Canterbury's Lake Ellesmere is the most important wetland habitat of its type in New Zealand. Photo / File
Canterbury's Lake Ellesmere is the most important wetland habitat of its type in New Zealand. Photo / File

A 1990 National Water Conservation Order declared it as an outstanding wildlife habitat.

Extensive wetlands around the lake margins acted as a filter and played an important role in maintaining water quality, but these had been largely drained.

Due to direct pressures in this over-allocated and intensively developed catchment like conversion to pasture, irrigation and heavy grazing, the area regularly experienced water quality issues like toxic algal blooms, which were hazardous to human and animal health.

Waikato still had the Ramsar-protected Whangamarino site, which stretched over 7000ha and was home to many rare plants and bird habitats.

But it remained in a degraded state.

Waikato still had the Ramsar-protected Whangamarino site, which stretched over 7000ha and was home to many rare plants and bird habitats. Photo / File
Waikato still had the Ramsar-protected Whangamarino site, which stretched over 7000ha and was home to many rare plants and bird habitats. Photo / File

Water drained into it from one of the country's most polluted lakes, Lake Waikare, and last summer the wetland became anoxic, oxygen depleted, causing thousands of fish to die.

"If an internationally recognised Ramsar wetland like Whangamarino is in such bad shape - what hope do our other wetlands have?" Cohen said.

"Regional councils must do more to protect wetlands, and that means better management of surrounding agriculture, enforcing rules to prevent illegal vegetation clearance and wetland drainage, and working with community, iwi, and DoC to restore wetlands that have become degraded."

AT A GLANCE: OUR LOST WETLANDS

• Nelson has lost the greatest proportion of its wetlands - 99.2 per cent.
• Southland has lost the largest area of wetlands in hectares (404,000 ) followed by Waikato (328,290)
• Otago has lost the least proportion of wetlands – only 76 per cent, but has still lost nearly 84,000ha of wetland.
• Southland has lost nearly 404,000ha of wetland.
• Canterbury has lost nearly 167,000ha of wetland.
• Auckland has lost 55,000ha of wetland.
• Overall, New Zealand has lost 2,221,304ha of wetland, and only 249,776 remain.