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Lake Onslow

Lake Onslow is a man-made lake formed in 1890 by the damming of the Teviot River and Dismal Swamp. The catchment of Lake Onslow is used predominantly for grazing.

Lake Onslow is a man-made lake east of Roxburgh and south of Alexandra in the Central Otago Region of Otago. It lies 700 m above sea level. It was formed in 1890 by the damming of the Teviot River and Dismal Swamp. Lake Onslow is set in wide open Otago tussock 700m above sea level. It is situated about 22km east of Roxburgh, at the northwest end of the Lammerlaw Range. The catchment of Lake Onslow has an area of 126 km2 and is used predominantly for grazing. Lake Onslow is a man-made, relatively shallow lake in an undeveloped high country catchment. However, in the last few years there has been some land use change in the lake’s immediate catchment from tussock to pasture. As a water body’s trophic state is largely determined by nutrient inputs from the surrounding catchment (Barnes, 2002), there is the possibility that the trophic state of Lake Onslow may change with agricultural intensification. The lake can currently be classified as being in an eutrophic state.

Lake Summary
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  • Catchment size
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  • Mixing pattern
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Scientific data for this lake

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

  • Water Quality

    Trophic Level Index (TLI)

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    The TLI score is an indicator of lake health and is determined from a suite of water quality measurements.

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    Trophic Level Index (TLI) history for this lake

    The TLI score for a lake is calculated from four water quality measurements – chlorophyll a, total nitrogen, total phosphorus and water clarity. If water clarity is unavailable, TLI is calculated using the other three water quality measurements. A higher score indicates poorer water quality.

    View a factsheet on TLI

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    TLI history for Lake Onslow
    Year

    What do the icons mean?

    VERY GOOD
    Very good water quality. Trophic Level Index of 0-2. Microtrophic lake conditions.
    GOOD
    Good water quality. Trophic Level Index of 2-3. Oligotrophic lake conditions.
    FAIR
    Average water quality. Trophic Level Index of 3-4. Mesotrophic lake conditions.
    POOR
    Poor water quality. Trophic Level Index of 4-5. Eutrophic lake conditions.
    VERY POOR
    Very poor water quality. Trophic Level Index of greater than 5. Supertrophic lake conditions.
    NO DATA
    No data available.
    TLI history for Lake Onslow data table
    Year TLI Score
    Year TLI Score
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  • 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
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    LakeSPI history for Lake Onslow
    Year

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