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Firth of Thames

The Firth of Thames is a large compound estuary and a drowned river valley. It has a catchment area of 4194 km2 and is the primary receiving environment for the Hauraki Catchment. The estuary is used for a range of recreational activities, harvesting of seafood and aquaculture. The south-western shore and Miranda Wildlife Refuge of the Firth of Thames is recognised as an internationally important wetland under the Ramsar Convention (one of six sites within New Zealand).

Historically the Firth of Thames received a high amount of sediment and nutrients from mining and land clearance in the catchment. The estuary is still under increasing pressure from human activities, including marine farming and the input of sediment and nutrients due to the intensification of farming and urban development within the surrounding catchment.

The Firth of Thames Ramsar site is ranked as one of New Zealand’s three most important areas for shorebirds (including migrant godwits and knots, and local birds such as the pied oystercatcher, New Zealand dotterel, variable oystercatcher and black-backed gull).


The estuary is also an important habitat for a range of common inshore fish species, many of them of cultural, recreational and commercial value. These include snapper, kingfish, jack mackerel, red gurnard, sand flounder and yellowbelly flounder. The Firth is also a nursery area for juvenile snapper, spotted dogfish, and hammerhead shark.


The Firth of Thames is a site of cultural significance to Hauraki iwi.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary

Overview

Estuary characteristics

  • Significant features
    • New Zealand’s largest shallow marine embayment
    • Miranda Wildlife Refuge (Ramsar site) - thousands of wading birds and shorebirds
    • Godwits - migrate annually between New Zealand and the Arctic
    • New Zealand’s largest mangrove forest (1374 ha)
  • Total area
    72910 hectares
  • Total shoreline length
    136km
  • Tide
    Tide range (m) (spring/mean/neap) - 2.86/2.45/2.05
  • Key rivers
    • Waihou River
    • Piako River
    • Kauaeranga River
    • Waitakaruru River

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. For example, the sandflats of estuaries surrounded by rural areas will typically contain contaminants related to rural activities (e.g., cadmium from crop fertilisers and copper from fungicides), whereas those surrounded by urban areas are more likely to contain contaminants associated with cities (e.g., zinc and lead from roads and building materials). 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.

Piako River
Kauaeranga River
Maukoro Canal
Waihou River
Waitakaruru River

What do the Broad Land Cover Classes mean?

Land cover information on LAWA is grouped into land cover classes at two levels of detail – broad and medium. For this overview we are showing the six broad-level classes for the catchment.

  • Forest

    Inclusive of; indigenous and exotic forest.

  • Scrub / shrubland

    Inclusive of; indigenous and exotic scrub / shrubland.

  • Grassland / other herbaceous vegetation

    Inclusive of; tussock and exotic grassland and other herbaceous vegetation.

  • Cropland

    Inclusive of; cropping / horticulture.

  • Urban / bare / lightly-vegetated surfaces

    Inclusive of; natural bare/lightly-vegetated and artificial bare surfaces, and urban area

  • Water bodies

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Monitored sites 5

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