Geologically, the Bay of Islands is an old river delta that “drowned” following rising sea levels after the last ice age about 12,500 years ago. This resulted in the creation of a large number of islands close to shore.
The area is characterised by a number of features: a large multitude of bays and estuaries carrying nutrient rich waters out to sea; and the sub-tropical East Auckland Current which brings warm water and associated marine fauna to the area during summer and autumn.
The Cape Brett peninsula (home to the Hole in the Rock) intersects this current, which means that the area becomes a large catchment for nutrients, thus attracting a wide variety of marine flora and fauna.
The Bay also boasts a great variety of habitats, each with a characteristic wildlife and dynamic. In fact, examples of all of New Zealand’s different marine habitat types can be found here.
Additionally, the Bay lies in the path of the migration routes of numerous seabird and marine mammal species. All this makes the Bay a particularly rich area for marine wildlife, and a paradise for lovers of the underwater world.