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Lake Horowhenua

Lake Horowhenua is a shallow coastal dune lake and the largest natural lake in the Manawatū-Whanganui Region. In 2013, Horizons Regional Council installed a continuous water quality monitoring buoy in the lake, and since then water samples have also been collected by boat or helicopter usually on a monthly basis. 

The lake catchment area is nearly 65 per cent pasture, which is a source of lake eutrophication (nutrient enrichment) that can lead to increased plant growth and/or algal blooms. The lake is located within a target catchment for nutrient management under Horizons Regional Council’s One Plan. Kākahi (native freshwater mussels), an important indicator of water quality, were observed by NIWA during a survey in 2017.

Nutrients from 25 years of treated sewerage discharge into the lake and ongoing land-use effects has led to the present hypertrophic condition (lakes that have been excessively enriched with nutrients). The lake has cyanobacterial blooms and a problem with dense weed growth that can interfere with contact recreation during summer. Efforts to clean-up the lake have been ongoing for several decades and include the establishment of a full native planting buffer strip around the lake, and a formal catchment management strategy being established by Horizons Regional Council.

Alongside the science and restoration efforts, several key partners have developed and signed the Lake Horowhenua Accord. Five parties representing the Muaūpoko owners, community interests and statutory bodies have agreed to work together to provide leadership to halt the degradation and put in place remedial measures that will begin to return Lake Horowhenua to a taonga (treasure) that holds pride of place in the Horowhenua community. The Lake Horowhenua Clean-up Fund was established in 2014. Primary projects in this work programme are to provide physical and infrastructural assets to address the key issues of toxic algal blooms including through lake weed harvesting, sediment and nutrient inputs to the lake from rural and urban sources, and to improve habitat and access to the lake for native fish.



Lake Summary
  • Lake size
  • Maximum depth
  • Catchment size
  • Mixing pattern
  • Geomorphic type
Scientific data for this lake

This dashboard shows information on the data collected by the regional councils and unitary authorities for two lake water quality and ecological condition measurements. LakeSPI (Lake Submerged Plant Indicators) and TLI (Trophic Level Index).  Select an indicator to see the historical monitoring data.

  • Water Quality

    Trophic Level Index (TLI)

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    This measure is the Trophic Level Index (TLI). The TLI indicates the life supporting capacity of a lake and is based on four water quality indicators.

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    Trophic Level Index (TLI) history for this lake

    Trophic Level Indicator (TLI) which measures four parameters: water clarity, chlorophyll content, total phosphorus and total nitrogen. From these parameters a TLI value is calculated. In cases where water clarity data is missing a three parameter TLI is calculated. The higher the value, the greater the nutrients and fertility of the water which encourages growth, including algal blooms. As a rule, higher TLI scores mean poorer water quality. View a factsheet on TLI

    TLI history for Lake Horowhenua

    What do the icons mean?

    Very good water quality. Trophic Level Index of 0-2. Microtrophic lake conditions.
    Good water quality. Trophic Level Index of 2-3. Oligotrophic lake conditions.
    Average water quality. Trophic Level Index of 3-4. Mesotrophic lake conditions.
    Poor water quality. Trophic Level Index of 4-5. Eutrophic lake conditions.
    Very poor water quality. Trophic Level Index of greater than 5. Supertrophic lake conditions.
    No data available.
    TLI history for Lake Horowhenua data table
    Year TLI Score
    Year TLI Score
  • Ecological Conditions

    Lake Submerged Plant Indicators (LakeSPI)

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    The LakeSPI status describes the ecological condition of the lake and is based on plants present.

    LakeSPI data provided by NIWA

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    LakeSPI history for this lake

    LakeSPI (Lake Submerged Plant Indicators) is a method of characterising the ecological condition of lakes based on the composition of native and invasive plants growing in them. A higher LakeSPI percentage result is associated with better ecological health:

    LakeSPI N/A
    LakeSPI {{spiData.details.Value}}%

    The overall LakeSPI score is calculated using a Native Condition Index ('good' plants) and an Invasive Impact Index (introduced, non-native plants):

    Native Condition N/A
    Native Condition {{spiData.details.NativeIndex}}%
    Invasive Impact N/A
    Invasive Impact {{spiData.details.InvasiveIndex}}% NA

    A higher Native Condition value indicates better ecological condition, but a higher Invasive Impact value indicates invasive plants are negatively impacting native plant communities.
    View a factsheet on LakeSPI for more information on these indicators.

    • LakeSPI
    • Native Condition
    • Invasive Impact
    LakeSPI history for Lake Horowhenua

    What is this graph showing me?

    This graph is displaying the overall LakeSPI score over time. The results denote the ecological condition of the lake.

    Excellent ecological health. A LakeSPI score of 75-100%.
    High ecological health. A LakeSPI score of 50-75%.
    Moderate ecological health. A LakeSPI score of 20-50%.
    Poor ecological health. A LakeSPI score of 0-20%.
    Non-vegetated. A LakeSPI score of 0% (there are no plants present).
    No data available.
    LakeSPI history for Lake Horowhenua data table
    Sample Date LakeSPI Status LakeSPI % Native Condition Index % Invasive Impact Index %
    LakeSPI information has been provided by NIWA.

Monitored sites on Lake Horowhenua

...retrieving sites.

No sites found.

Live Data


The Environmental Data produced by this page should be used as a guide only. LAWA takes no responsibility for the accuracy of information presented, and accepts no liability for actions taken of others based on this information.