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Te Awarua-o-Porirua Estuary

Te Awarua-o-Porirua Harbour is a large, well flushed tidal lagoon estuary. The harbour is made up of two estuaries, the Onepoto arm and the larger Pāuatahanui arm, each of which are fed by a number of small streams and are connected by a narrow channel at Paremata.

Although the harbour has a large, shallow subtidal area that makes up more than 60% of the estuary, water is completely flushed from both estuaries in less than three days. The large intertidal area supports extensive seagrass meadows and shellfish beds.

Greater Wellington has carried out annual environmental monitoring at five subtidal sites since 2004. This includes two Onepoto sites (Porirua sites 1 and 2) and three Pāuatahanui sites (Pāuatahanui sites 1, 2 and 3).

In 2008 four additional intertidal sites were added to this monitoring programme. These include: Onepoto sites (Onepoto A and B), and Pāuatahanui sites (Pāuatahanui A and B).

Te Awarua-o-Porirua Harbour has been extensively modified over the years, particularly the Onepoto arm where almost all of the historical shoreline and salt marsh has been reclaimed for roading and development. Most of the arm is now lined with steep straight rock walls flanked by transport corridors. The Pāuatahanui arm is slightly less modified, with areas of salt marsh remaining in the north and east on the seaward side of the road.

Catchment land use in the Onepoto arm is dominated by residential and commercial development. In the steeper Pāuatahanui arm grazing is the dominant land use, although residential development is significant in some areas.

Sedimentation is a major problem in the estuary, particularly in the Pāuatahanui arm, where potential sources include land disturbance associated with residential and road development.

Elevated nutrient inputs are also causing moderate degradation of estuary health by decreasing sediment oxygen levels and encouraging algal growth.

Results: Intertidal monitoring sites

Intertidal sediment quality in Te Awarua-o-Porirua Harbour is generally ‘good’, with low levels of nutrients and metal contaminants.

Monitoring has identified a gradual decline in species at all sites except at the site near Porirua City. This is consistent with sedimentation monitoring that reveals a long-term harbour-wide increase in the extent of mud-dominated sediments.

Results: Subtidal monitoring sites

Sediments at all subtidal sampling sites are muddy, except for the site located off Camborne, which is sandy. The muddy sediment concentrates contaminants from rivers, stormwater, and road runoff in the deeper muddy areas in the Onepoto arm and at the southern end of the Pāuatahanui arm.

Overall, sediment in the Pāuatahanui arm was found to have lower levels of contaminants than the Onepoto arm. This is likely due its distance from the Porirua City Centre and the concentration of urban and industrial sources of pollution. Ecologically, the Onepoto subtidal area scored lower than the Pāuatahanui subtidal area, with fewer species of sediment dwelling invertebrates found closer to the city.

Species in the Onepoto arm generally limited to those that can tolerate mud and disturbances. Despite this lack of diversity, there are double the number of animals in the Onepoto arm compared to the Pāuatahanui Arm.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary


Estuary characteristics

  • Significant features

    Te Awarua-o-Porirua Harbour is the largest estuarine ecosystem in the lower North Island.

    The Pāuatahanui arm is a nationally significant estuarine area.

    Te Awarua-o-Porirua Harbour has the largest proportionate subtidal area of any estuarine ecosystem in New Zealand.

  • Total area
    807 hectares
  • Tide
    Tidal influence
  • Flushing time
    Three days
  • Key rivers
    • Duck Creek
    • Porirua Stream
    • Pāuatahanui Stream
    • Kakaho Stream
    • Horokiwi Stream

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 9

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