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The Whangateau estuary is a permanently open tidal lagoon on the northeast coast. The estuary is highly valuable for wildlife, providing rich feeding grounds for many migratory and endemic shore birds. In the upper reaches of the harbour an ecologically significant sequence of seagrass and mangroves transition into saltmarsh and coastal kahikatea swamp forest (Omaha Taniko Wetlands Scientific Reserve).

Freshwater inputs to the estuary are low and over 90% of the estuary’s volume is flushed during each outgoing tide. Native forest covers a quarter of the catchment, with rural land uses and exotic forest making up the rest. The monitoring sites have low mud content in comparison to other estuaries in the region and the estuary is in good overall health.

Intertidal sandflats cover 85% of the area, supporting abundant and diverse communities of macrofauna. A causeway in the mid reaches dissects the harbour altering natural hydrodynamics.

Horseshoe Island, and the surrounding sandflats in the harbour’s lower reaches provide a breeding site for a colony of ‘nationally vulnerable’ Caspian tern, while a pied shag colony, also ‘nationally vulnerable’, is present at Ti Point and the mouth of the estuary.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary


Estuary characteristics

  • Significant features
    • Over 90% of the water is flushed during each tide
    • Approximately 85% of the estuary is intertidal
    • Omaha Taniko Wetlands Scientific Reserve
    • Omaha Spit Reserve
    • Omaha Sequence biodiversity focus area
    • Within the Hauraki Gulf Marine Park
    • Significant Ecological Areas identified within the estuary as defined in the Auckland Unitary Plan


  • Total area
    750 hectares
  • Total shoreline length
    36 km
  • Key rivers
    • Omaha River
    • Waikokopu Creek

What's happening upstream?

See results from monitored river quality sites influencing this estuary

River quality

What's happening upstream?

The physical characteristics and health of estuaries are influenced by the rivers and streams flowing into them. For instance, when it rains the mud and contaminants generated on land can be washed into rivers and eventually flow into the estuary. The health of our rivers and streams can therefore be very important for Estuary Health, and understanding the upstream pressures can help with interpreting estuary monitoring data.

Monitoring is undertaken for a range of river health indicators (e.g., water quality and ecology) in many catchments across the region. Where there are monitored river catchments that influence this estuary, these are shown below. You can click through to view monitoring results from these River Quality sites to see current state and how health has changed over time.

What surrounds my estuary?

See land cover information from monitored catchments that surround this estuary

Land cover

What surrounds my estuary?

The physical characteristics and health of estuaries are influenced by local geography and the way we use our land. This is because estuaries are the receiving environments for many of our land use activities. Land cover information can be used as an indicator of land use, therefore knowing the surrounding land cover can help us understand which pressures might be affecting Estuary Health.

Where there is land cover information available for nearby catchments, these are listed below. These figures show the types of vegetation and built or natural features that surround the estuary margins and the rivers that flow into this estuary. You can click through to the Land Cover topic to see these land cover classes broken down into further detail, and view changes over time.

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Monitored sites 4

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