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Freshwater Estuary

Freshwater Estuary is a relatively large, minimally disturbed “tidal river plus intertidal delta” type estuary that has established within the confines of Paterson Inlet. Fed by the largest river on Stewart Island, Freshwater River, it drains the native forest catchment of the Mt Anglem highlands and Ruggedy Mountains area. Its lower reaches meander across Freshwater Valley, the largest area of flat land on Stewart Island. The estuary itself is relatively shallow, with a mean depth of approximately 2m, and has an extensive intertidal area where 77% of the estuary is exposed at low tide, and supports very large areas of seagrass.

As Freshwater Estuary lies within Rakiura National Park and the waters of Te Whaka a Te Wera Mataitai Reserve, there is little potential for direct human modification of this estuary, salt marsh or terrestrial margin, and past habitat disturbance has been minimal. Consequently, it provides an important reference system against which to assess the condition of other estuaries in Southland and New Zealand.

Monitoring is carried out in the Freshwater Estuary at three sites. Site A and B have been monitored since 2009, while site C has been monitored since 2020. They are sampled once each year (during summer) for mud content, trace metals in sediment, and macrofauna along with other sediment characteristics.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary


Estuary characteristics

  • Total area
    812 hectares
  • Key rivers
    • Freshwater River
    • Tolson 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.

Monitored sites 3

Select a monitored site from the list below

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