Human activities generate a variety of toxic heavy metals and other compounds that are used in the coastal environment (e.g., anti-fouling paints, oils and fuels), or which enter coastal waters through spills, storm water run-off and wastewater discharges. The main causes of contamination in the Hauraki Gulf Marine Park are urbanisation, historical mine activity, and agriculture. Major spills sometimes have immediate and catastrophic effects. These tend to be obvious and localised. Contaminant loads from individual sources such as port, industrial and mine activities, marinas and landfills, can also be very high and persistent, causing localised impacts. But many contaminants come from small sources scattered throughout catchments, which combine to produce large loads that affect broad areas in harbours and estuaries.
Contaminants commonly bind to sediments and other particles, which settle out and accumulate on the seabed. Elevated contaminant concentrations in coastal sediments affects the survival, reproduction and/or behaviour of animals that live on the seabed, and may cause flow-on effects on other parts of the ecosystem, natural character or amenity values. Māori are particularly concerned about effects on the mauri (life force) of the coastal areas, and the health, abundance and safety of kai moana for consumption. Primary contaminants of concern are the heavy metals, copper and zinc, with lead and mercury of secondary concern. Other contaminants may also accumulate, including new contaminants that are constantly emerging. Environmental scientists are struggling to keep pace with the rapidly increasing list.
Protection and restoration efforts have been given a boost by the recent (October 2025) Hauraki Gulf/Tikapa Moana Marine Protection Act which aims to reverse decades of ecological decline.
There are now 12 High Protection Areas, 5 Seafloor Protection Areas and 2 Marine Reserve Extensions.
The Act also acknowledges the role of mana whenua as Kaitiaki (guardians) introducing -
Customary Practices: Authorised customary fishing is permitted in HPAs to support Māori cultural practices.
Active Restoration: Iwi are actively involved in projects such as restoring mussel beds and managing the removal of kina barrens.
Rāhui: Iwi have placed rāhui (temporary closures) to protect struggling shellfish beds.
