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Lake Rototoa

Lake Rototoa is a large, deep lake located behind a series of dunes in the South Kaipara Heads area. It has the best water quality of the lakes monitored by the Auckland Council and remains as one of Auckland’s gems.

Lake Rototoa is one of the largest and deepest lakes monitored by the Auckland Council. This deep monomictic lake has less than 40% of its catchment being used as pasture. The lake regularly stratifies causing anoxic bottom waters. It is the cleanest lake monitored by the Auckland Council and is classified as mesotrophic. The respective catchment has relatively steep slopes at the lakeshore and this effectively prevents stock from entering the area around the lake. The lake catchment has farmland on the eastern side and exotic pine forest on the western side with a crown reserve on the western shores. The monitoring data indicates that a milder climate and possibly land use (forestry practices) are causing the lake water quality to deteriorate. Specifically, these are reducing hypolimnetic oxygen concentrations in summer allowing sediment nutrient release. A consequence of this is a decrease in water clarity although this may be augmented from silt erosion associated with the dominant land uses. The lake also boasts a diverse native plant community and is dominated by rotifers indicative of a low trophic state. There has been historic evidence of elevated nutrient concentrations stimulating algal growth and resulting in a decrease in water clarity which was interpreted as a sign of deteriorating water quality. In recent years the surface waters showed an improvement in water clarity and a possible improvement in total phosphorus and trophic level index (TLI). There has also been a decline in nitrate concentrations and an increase in dissolved oxygen. The bottom waters exhibited decreasing concentrations of total phosphorus, nitrate and ammonia. Contrary to these improvements in water quality an increase in total suspended solids and turbidity in the lake have been noted. Hornwort was found in the lake in 2007 and despite various control measures implemented by the Auckland Council the establishment of this invasive plant could not be controlled. Lake Ototoa appears to be relatively stable however the establishment of invasive organisms, namely Hornwort and Rudd, are a definite cause for concern.

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 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

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

    What do the icons mean?

    Very good water quality. Trophic Level Index of less than 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.
  • 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 %
    LakeSPI history for Lake Rototoa
    LakeSPI history for Lake Rototoa 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 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.

Monitored sites on Lake Rototoa

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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.
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