An $800 million pipeline from Western Springs to the Mangere Sewage Treatment plant is described as "Auckland's most expensive freshwater river" by one of the groups opposing it.
The Watercare proposal for the 13km "central interceptor" to catch sewer overflows has drawn 750 submissions - 600 of them objections voiced via a form which was on the website of residents' groups.
The Manukau Harbour Restoration Society is making a joint submission with the Mangere Bridge Residents & Ratepayers Association and the Onehunga Enhancement Society.
The giant engineering project's request for land designations and consents and a network discharge consent was publicly notified in October and submissions closed in December.
Auckland Council has appointed a panel of independent commissioners to hear the case for granting the application and objections.