Manukau Harbour Protection Society incensed at having to take Waitemata wastewater.
Groups promoting Onehunga as a seaside town and the Manukau Harbour as a haven for recreation and wildlife are raising $140,000 for a court appeal against a $950 million sewer tunnel project.
"Come to our bake sale," said Bronwen Turner, of the Manukau Harbour Protection Society.
"It's a huge responsibility for a non-profit community organisation to take on but people are aghast when told about the project."
Last month, Auckland Council-owned Watercare Services was granted resource consents to start boring for the Central Interceptor Project in 2017.
Watercare said the council's hearings commissioners' approval showed its plan for the 13km storage tunnel from Western Springs to the Mangere treatment station was the best way to serve a growing population and reduce sewer overflows and construction nuisance.
However, Ms Turner said an appeal had been lodged with the Environment Court by her society, as well as the Onehunga Enhancement Society and the Mangere Bridge Residents & Ratepayers Association.
The groups could not stand back and let the Waitemata Harbour and its beaches be cleaned up by Watercare bringing more wastewater over to the Manukau Harbour instead.
"They don't have any similar initiatives within the project to clean up the Manukau.
"Where is the full discussion on alternatives to this combined sewer-stormwater tunnel? We were just told that this was it."
Ratepayers' Association spokesman Roger Baldwin said the project's costs would pass to those who had already paid in their rates for their areas to have separation of sewage and stormwater pipes.
"It's a crazy process when it is the applicant's boss [Auckland Council] granting resource consent."
About 700 submissions opposed the project.
The commissioners imposed additional conditions on Watercare's insistence on the tunnel having an emergency overflow device, which harbour society chairman Jim Jackson said had the potential to undo years of improving harbour water quality.
Watercare Services resource consents manager Belinda Petersen said it would not appeal against any of the conditions. She said the commissioners had agreed the Central Interceptor was the best option.