Forest & Bird environmental lawyer Sally Gepp said she was "shocked" to see Auckland Council celebrating the work.
"We have a biodiversity crisis in New Zealand, and the world, and poor monitoring and enforcement of rules to protect the environment is a major contributor of loss," Gepp said.
"Mangroves are amazing native plants that have important roles in the environment.
"They protect our coastal communities from inundation from the sea by slowing down waves and absorbing flood waters, they absorb carbon from the atmosphere to help prevent climate change, and provide essential nursery habitat for fishes, and feeding grounds for native birds like at-risk banded rail."
New Zealand's single mangrove species, Avicennia marina - mānawa in Māori - has been present here for at least 14,000 years. Other species had existed here over millions of years.
Gepp said the expansion of mangroves in some areas, such as Waiuku, was due to sediment running to the sea and unhealthy rivers.
"It is understandable communities are annoyed there is more mud than there used to be, but removing the mangroves will not resolve the sediment issue, it will only wreck native habitats and destroy the natural flood and storm protection mangroves provide."
The media release said Auckland Council provided about $10,000 a year to the group for its work, including chainsaw maintenance.
Forest & Bird wanted to see Auckland Council engage an ecologist to review the consents to ensure the activities were not causing damage to banded rail habitat.
Waiuku resident Ian Scobie, who started the mangrove removal project initially to clear a passage for him to kayak into the estuary, said from their observations the removal had improved the environment.
"We found as we cleared the areas we got very positive effects, with fish, birds, crabs - you name it - returning, plus the added improvement of the human environment with boating and the aesthetic appearance."
Scobie said they had been planting the shoreline in native rush species, those that were there prior to the mangroves, to counter erosion and sediment entering the estuary, and to enhance the banded rail habitat.
"We believe the rushes are actually a better habitat for the banded rail than the mangroves."
Scobie, whose home backs on to the water's edge, said the rushes were better than the mangroves at countering storm surges and impending sea level rise.
"We find that rushes dampen the surges much better than mangroves."
Auckland deputy mayor Bill Cashmore, who had been involved with the group over the past five years, said the removal had been done in a staged approach with "rigorous" consent conditions, to minimise any environmental damage, including to banded rail habitat, and to ensure areas were adequately replanted.
The area was free of mangroves until the late 1970s, and once had plenty of white, sandy beaches, Cashmore said.
Previously "uncontrolled development" in the area, prior to the Resource Management Act, had seen top soils washing off the land and into the sandy estuary, allowing the mangroves to flourish.
"It used to be awful. But what we have seen since the Mudlarks began their volunteer work is it slowly returning to how it was. The wildlife is improving, areas are being replanted and pathways are going in, all with volunteer labour. It is something to be celebrated.
"It will be a long time before we get back to those sandy beaches, but we have very strict sediment controls in force now."
University of Auckland Associate Professor Carolyn Lundquist, who also works for Niwa, said while mangroves were declining globally, in New Zealand, areas were increasing on average about 3 per cent annually.
Mangroves had been in New Zealand for millions of years, but had accelerated recently due to land use changes increasing the amount of sediment in harbours and estuaries, and developments - such as building motorways - that disrupted water flow.
Mangroves could be removed if done appropriately with a long-term plan and appropriate planting of other species, Lundquist said.
"A lot of places where they have been removed are still muddy. The key is making sure there is a long-term view. It is a balancing act between community interests and environmental concerns, and not just about making it look good, but healthy."
Niwa had developed a set of guidelines and had worked with Auckland Council and various community groups on how to remove mangroves in the wider Manukau Harbour appropriately, Lundquist said.
