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Tokomairiro Estuary

Tokomairiro Estuary is a modified, moderate-large sized tidal river located downstream of Milton. The tidal mouth though often constricted, is nearly always open, while the upper estuary is at times poorly flushed, stratified/layered and susceptible to phytoplankton blooms. The estuary substrate is dominated by muddy sediments but supports large areas of saltmarsh, subtidal macrophyte growth, and small beds of nuisance macroalgae. The 398km2 catchment is dominated by high producing exotic pasture (54%) and plantation forestry (35%).



The estuary supports a variety of substrate types (the base on which an organism lives), extensive areas of salt marsh, very small areas of intertidal seagrass (Zostera), but large subtidal macrophyte beds (Ruppia).

It has excessive muddiness throughout most of the upper and middle estuary, a moderate level of eutrophication, and large areas with low sediment oxygenation.

Historically, there has been significant modification and loss (~90-100 hectares) of estuary salt marsh through drainage and reclamation, and the 200m terrestrial buffer is now dominated by pasture and plantation forest.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary


Estuary characteristics

  • Significant features
    • Contains large areas of the native macrophyte Ruppia growing subtidally
    • Important habitat for coastal birds including waders, shorebirds and waterfowl
    • Extensive high-value salt marsh habitat
  • Total area
    150 hectares
  • Key rivers
    • Tokomairiro 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.

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.

Tokomairiro 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
Monitored sites 3

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