It has an area of 4000 km2,[1] and lies between, in anticlockwise order, the Auckland Region, the Hauraki Plains, the Coromandel Peninsula, and Great Barrier Island.

[4] In traditional legend, the Hauraki Gulf is protected by a taniwha named Ureia, who takes the form of a whale.

[7] Prior to the Oruanui eruption 27,000 years ago, the Waikato River also flowed into the Hauraki Gulf at the Firth of Thames.

This river flowed north, along the plains, turning east and exiting towards the Pacific Ocean along the modern-day Colville Channel between the Coromandel Peninsula and Great Barrier Island.

In January 2018, huge swells in the Hauraki Gulf caused widespread damage to its coastal areas and in only a few hours, the coastline or Otata had been reduced by up to 5 meters, exposing the midden.

The aim of the excavation was to record this information before it is lost to erosion and was carried out in partnership with Ngāi Tai ki Tāmaki, the landowners.

The migratory canoes Tainui and Arawa left Raiatea at similar times, and both explored the Bay of Plenty area.

[13]Among larger cetaceans, Bryde's whales are residents and relatively common in the Gulf, and their presence in these busily travelled waters leads to a large number of ship strikes, with sometimes several of the whales dying each year from collisions with shipping vessels or sport boats.

[11] In recent years, increases in numbers of migrating baleen whales are confirmed long after the end of hunting era.

[16] Many of the islands are official or unofficial bird sanctuaries, holding important or critically endangered species like kiwi, takahē, brown teal and grey-faced petrel.

Although major study by the Hauraki Gulf Forum in 2011 found that all environmental indicators were still worsening or stable at problematic levels, voluntary coast clean-up groups have collected about 450,000 litres of litter collected from the shoreline, although further conservation efforts are required to maintain the environmental integrity of the gulf.

This severe overfishing, which unbalanced the marine environment by the removal of a main predator in the food chain, led to further degradation, such as a widespread disappearance of kelp beds as they were overtaken by kina barrens.

[18] Also particularly damaging are the results of nitrogen carried into the gulf from surrounding agricultural land, with almost 90% coming from the dairy-farming runoff into the Firth of Thames.