Pierre and Jackie Chatelanat spent 50 years transforming their 843ha Kaipara Harbour farm into something worth preserving.

It was a lifetime project, and now the Tapora Peninsula property is worth $10 million.

Located 100km north of Auckland, it has sweeping views over the harbour, bush, wetlands and sandy beaches. In order to keep it that way, the Chatelanats gifted it to the nation, no questions asked, no strings attached, and with a minimum of fuss - they have declined any media interviews.

The couple, both in their mid-70s, decided in October that giving away the property as a regional park was the best way to preserve and protect it.

Pierre Chatelanat has owned the property since he came to New Zealand in the early 1950s, when it was covered in manuka and gorse.

It is the largest gift of land in the Auckland region since Sir John Logan Campbell donated Cornwall Park to the city in 1901. A spokesman for the couple said they were passionate about the environment and the Kaipara Harbour.

The couple retired in 1998 and live quietly in a house they built on a secluded part of the farm. They have no children. They enjoy trips to Auckland for the opera and drive an unpretentious Toyota car into Wellsford for fortnightly shopping trips.

Their sweeping property will become the 23rd Auckland Regional Park. It is expected to be formally opened to the public in 2011.

The Chatelanats should be left in no doubt that a city will be forever grateful.