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Waimea Inlet

The Waimea Estuary is the second largest estuary (3,462 ha) in the South Island and located between Nelson-Richmond and Mapua. It is a shallow, tidal lagoon type estuary with a large barrier sand island (Motuora/Rabbit Island) separating the estuary from Tasman Bay. The relatively large Waimea River flows into the estuary in the middle and flows out each side of Motuora/Rabbit Island. Many small hill-fed streams and a few important spring-fed streams also flow into the estuary. The estuary almost completely drains at low tide (<20% is sub-tidal).

The estuary has been extensively modified, current catchment landuse is 33% indigenous forest, 32% exotic forest, 20% productive grassland, 4% crop/orchard/vineyard, 3% urban.

The input of mud-dominated sediment appears to be largely historical, with anecdotal reports of high inputs sourced, in part, following the development of orchard land in the 1950’s and 1960’s. Seagrass beds are sparse across the estuary, covering ~2% of the intertidal area and located almost exclusively near the well-flushed entrance channel and central basin of the eastern arm. There has been a decrease in the extent of the beds since 2014 (largely attributable to improved mapping accuracy), and >60% reduction since the first records in 1990 (reflecting actual losses).  Nuisance opportunistic algal growths are uncommon, but a few localised hotspots (~20ha) occur (mainly of the red seaweed Gracilaria chilensis). Salt marsh remains a significant feature of the estuary (~10% of the intertidal) and is dominated by herbfield species. However, its prevalence is greatly reduced from its assumed historic extent through drainage, reclamation, margin development and channelisation. Since 1946 there has been a further reduction in salt marsh area of ~24%. Currently, initiatives are underway to enhance or restore some of this high-value habitat. The terrestrial margin bordering the estuary is highly modified and comprises very few habitat features that are in their natural state. Only 18% of the 200m-wide margin was classified as densely vegetated in 2020, the majority of which is exotic forestry. In many areas the terrestrial margin has been highly modified by roading, causeways, seawalls, reclamations, or land clearance.

TDC and NCC have conducted broad-scale mapping using the National Estuary Monitoring protocol in 1999/2001, 2006, 2014, and 2020 and fine-scale surveys in 2001, 2006, 2014, 2015, 2016.

Overall, despite extensive historical habitat modification, significantly reduced habitat diversity, and large areas of mud-dominated sediments, Waimea Inlet retains many areas of very significant ecological value. However, the prevalence of mud-dominated substrate, the persistence of localised dense macroalgal beds, and pressures on salt marsh near the estuary margin from drainage and reclamation are key broad scale habitat stressors that threaten these values. Salt marsh losses are likely to increase in future in response to sea level rise due to the current limited capacity for landward migration. Reductions in sediment loads, and targeted management of localised nutrient inputs, will be required to improve estuary condition.

Estuary summary

What makes my estuary unique?

Explore the characteristics of this estuary

Overview

Estuary characteristics

  • Total area
    3462 hectares

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.

Waimea River
Borck Creek
Reservoir Creek

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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