Ten million years ago, these islands were formed by a volcanic eruption. They are located about 25 kilometres off the east coast of Northland and form a chain about 10 kilometres long. In 1981, together with their surrounding waters, the Poor Knights Islands were established as a marine reserve.

Until about 200 years ago these islands were inhabited by Maori, unfortunately a tragic sequence of events led to a massacre and the islands were declared tapu (sacred.)

Biologically and ecologically, these islands differ in most respects from all other islands in New Zealand. The two large islands, Tawhiti Rahi to the north and the southern Aorangi, and various reefs and inlets are in the path of the East Auckland Current, which flows along the edge of Northland's continental shelf. This warm water provides a pathway for tropical and sub-tropical visitors to settle.

The underwater landscape mirrors the steep and rugged land above water. South Harbour, Nursery Cove, Bartle's Bay, Cleanerfish Bay and Lighthouse Cove are shallow rocky reefs. The steep cliffs, which fringe the islands, can plunge vertically 100 metres to the sandy sea floor. There are more than 25 caves and archways around the Poor Knights, including Northern Arch, Middle Arch, the completely submerged Airbubble Cave and Rikoriko cave, the largest sea cave in the world. Other caves penetrate more than 50 metres into the islands and have not been fully explored. Together, these provide a diverse range of habitats found in no other single place.

At the Poor Knights you will see a spectacular diversity of plants and animals. Some of the lushest and densest kelp forests in New Zealand can be found at Cleanerfish Bay and Nursery Cove. You will find colourful invertebrates and benthic algae in the shade of the beds and feathery green sea rimu in the sand pockets between the boulders. You may also encounter sponges and gorgonians, tropical sea urchins, several species of starfish and brittle starfish.

The walls and archways offer a unique alternative to normal reef diving. On the upper areas of the walls, multi-coloured jewel anemones are common; lower down red, yellow and green encrusting sponge species. Mobile invertebrates include crabs, shrimps, Spanish lobsters, crayfish, snails, nudibranchs, crinoids and brittlestars.

It is impossible not to be dazzled by the vast schools of fish and the colourful wrasses. Snapper, trevally, marblefish, red moki, kingfish, blue cod and leatherjacket, to name but a few.
Tropical coral reef fish ride the current as larvae and settle here in midsummer; these include moon wrasse, sunset wrasse, and Lord Howe coral fish, pelagic species that could be encountered are striped marlin, yellowfin tuna and sunfish.

In shallow water, you will see demoiselles, black angelfish and Sandager's wrasse; between 15 and 30 metres pink and blue maomao, butterfly perch and schools of snapper, pigfish, rainbowfish, toadstool grouper and john dory.
Large short tailed stingrays are frequent visitors; sharks are more occasional visitors including shortfin mako, hammerhead and thresher. The most common sharks at the Poor Knights are carpet sharks and bronze whalers.