Akaroa harbour in Canterbury is to be designated a marine reserve.
A formal application for the reserve was lodged in 1996 by the Akaroa Harbour Marine Protection Society.
Former Minister of Conservation Kate Wilkinson denied the application two years ago, but a High Court ruling forced her to revisit that decision in May last year.
Current minister Nick Smith announced the designation in Akaroa on Sunday afternoon.
Dr Smith said he has carefully considered arguments from supporters and opponents.
The formal consultation had 2334 submissions in support and 709 objections, with the principal opponents being Ngai Tahu and recreational fishers.
Dr Smith says he has not upheld the objections but has decided to adjust the northern boundary by 55 hectares, reducing the reserve to 475 hectares.
The final stage, subject to consideration, is a formal recommendation by the Governor-General.
The Department of Conservation will review the reserve in a decade.