Local iwi have reached a major milestone with Auckland Council, to protect a culturally significant island in the Manukau Harbour.

The council has agreed Puketutu Island will now be governed by an independent trust, rather than a council-controlled organisation.

CCO committee deputy chairman Calum Penrose says council and iwi representatives will oversee issues like the depositing of wastewater biosolids.

"A number of key components, iwi in particular, are working together in a collaborative way to move the island forward."

Legislation may be required, to allow the trust to remain independent over the long term.