A formal celebration will be held on a boat to mark the new Akaroa Marine Reserve in the seaside town's harbour on Sunday.
An application for the reserve was lodged in 1996 by the Akaroa Harbour Marine Protection Society.
A High Court ruling forced a previous conservation minister to review a decision to decline it before current minister Nick Smith agreed to the designation in December last year.
It has been a contentious process - the formal consultation had more than 2300 submissions in support and 700-plus objections, with the principal opponents being Ngai Tahu and recreational fishers.
Dr Smith, along with Environment Minister Amy Adams, formally opened the reserve from a boat on Sunday morning.