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Lake Rotomanuka

Lake Rotomanuka is a complex of two lakes near Ohaupo, about 12km south of Hamilton. At 27,000 years, it is the Hamilton basin’s oldest lake, as well as the deepest. It is administered by the Department of Conservation as a wildlife management reserve. It is identified as a significant wetland in the Waikato Regional Plan.

The lake lies on the edge of the Moanatuatua peat bog, which has been largely drained for agriculture. The wider catchment is predominantly used for intensive dairy farming. Through drainage, the lake became two separate lakes, known as Rotomanuka North and South (or Gin Lake), linked by a 10ha wetland.

North Lake has far better water quality than South Lake, which was extremely nutrient enriched when last surveyed (in 2001). This difference is likely to be influenced by differences in the bathymetry of the two lakes. Submerged plants collapsed in the lakes in the late 1990s.

Exotic fish, particularly rudd, appear to be a major impediment to re-establishing submerged vegetation in the lake. Lake Rotomanuka is fully fenced to exclude stock. Waipa District Council has acquired several esplanade reserves to extend the width of the margin. Despite this, the lake margin is still narrow in places and would benefit from further extension, particularly in the area between the two lakes.

The effects of non-point source agricultural discharges, and invasive plant and animal pests are the main pressures upon the lakes and their margins. Various projects have been undertaken recently within the lakes’ catchment to improve the condition of the lakes, including development of:

  • farm and nutrient management plans for farm properties
  • a Community Catchment Action Plan for the lakes’ catchment by NZ Landcare Trust, which has involved the construction of silt traps and constructed wetlands on key inflows to reduce sediment and nutrient inputs to the lakes
  • a 10 year restoration programme for the lakes that will be undertaken through the Living Water programme, a Fonterra and Department of Conservation partnership.
Lake Summary
  • Lake size
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  • Maximum depth
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  • Catchment size
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Scientific data for this lake

This dashboard shows information on the data collected by the regional councils for two lake water quality and ecological condition measurements. Lake SPI (Lake Submerged Plant Indicators) and TLI (Trophic Level):

  • Water Quality

    Trophic Level Index (TLI)

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    This measure is the Trophic Level Index (TLI). The TLI indicates the lifesupporting 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

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    TLI history for Lake Rotomanuka
    Year
    TLI history for Lake Rotomanuka data table
    Year TLI Score
    Year TLI Score

    What do the icons mean?

    VERY GOOD
    Very good water quality. Trophic Level Index of less than 2. Microtrophic lake conditions.
    GOOD
    Good water quality. Trophic Level Index of 2-3. Oligotrophic lake conditions.
    AVERAGE
    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.
  • Ecological Conditions

    Submerged Plant Indicators (SPI)

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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.grades[0].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.grades[0].NativeIndex}}%
    Invasive Impact N/A
    Invasive Impact {{spiData.grades[0].InvasiveIndex}}%

    A higher Native Condition percentage is also good, but a higher Invasive Impact percentage is bad. View a factsheet on SPI

    • SPI %
    • Native Condition %
    • Invasive Impact %
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    LakeSPI history for Lake Rotomanuka
    Year
    LakeSPI history for Lake Rotomanuka data table
    Sample Date Status LakeSPI % Native Condition Index % Invasive Impact Index %
    LakeSPI information has been provided by NIWA.

    What do the icons mean?

    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.

Download Data

.ZIP file of lake data.
Download
Disclaimer

 LAWA Partners shall not be liable, whether in contract, tort, equity or otherwise, for any loss or damage of any type (including consequential losses) arising directly or indirectly from the inadequacy, inaccuracy or any other deficiency in information supplied irrespective of the cause.  Use of information supplied is entirely at the risk of the recipient and shall be deemed to be acceptance of this liability exclusion.

Sites

Monitored sites on Lake Rotomanuka

...retrieving sites.

No sites found.

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