Conservationists fear an expressway planned for the Kapiti Coast will run through the habitat of a critically endangered duck.
But the New Zealand Transport Agency (NZTA) says the birds will be provided with a bigger and better area, under mitigation measures to protect the environment.
Kapiti Coast resident and conservationist Derek Schulz said he filmed about a dozen New Zealand grey ducks, or parera, over the last year at the Raumati Beach dune lake wetland environment.
NZTA has proposed a 16km expressway be built from McKays Crossing (Raumati South) to Peka Peka, north of Waikanae, which is on track to go through the wetland.
The road was part of the Wellington Northern Corridor, a development considered to be of national significance.
A board of inquiry, chaired by High Court judge Sir John Hansen, has received 728 public submissions on the proposal.
Mr Schulz said there was a huge variety of native birds at the wetlands.
"But the curious thing was to find these parera."
It looked like two females were raising chicks in the lake, he said.
"So we settled down to look at them and film them and over about a process of about a year it became very clear that we've got a group of about 10 or 12 that seem to be surviving on their own."
The bird was critically endangered because they would often interbreed with mallards, but these ducks weren't doing that, Mr Schulz said.
Massey University senior lecturer of agriculture and environment Phil Battley said because of the outbreeding with mallards, it was very rare to find a pure grey duck.
"The future is very bleak for them in New Zealand unfortunately."
The population was on a trajectory that would mean the population would end up "very low" if things kept going the way they were, Dr Battley said.
An expressway going through their environment wouldn't help, he said.
The Mahara Gallery in Waikanae is exhibiting films and photographs of the wildlife in the area, which include the parera, the grey teal, Australasian shoveller, pukeko, NZ scaup, white faced heron and royal spoonbill.
Janet Bayly, from the gallery said the project was a celebration of the wildlife at the lake, as well as "an obituary for it".
"It became clear by late February 2012 that the Kapiti Expressway was going to destroy this remarkable wetland."
Stephen Fuller, from NZTA, made a submission to the board which showed how damage to the wetlands could be mitigated.
He said the expressway affects only 5.6ha of indigenous vegetation and wetland habitat.
NZTA planned to replant 30.8ha to restore or recreate a range of habitats for birds and lizards and would support a number of stream restoration and wetland development projects.
"I believe this level of mitigation is entirely appropriate."
The combined area of indigenous habitat that will be created along the project alignment would be 96ha, he said.
"This is over 15 times the area of indigenous habitat loss.
"For this reason, it is my view that not only will effects be mitigated, but there will be a net ecological benefit."