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Lake Rotorua

Lake Rotorua is the region’s oldest lake. It is thought to have formed shortly after the Mamaku Ignimbrite eruption about 140,000 years ago, and it occupies a caldera created by the event. The lake has a 45m-deep crater north of Sulphur Point but is otherwise relatively flat-bottomed, with its deeper contour at around 26m, west of Mokoia Island. At 80sq km, Lake Rotorua has the largest surface area of the district’s lakes. It also has the largest catchment area at about 508sq km. Pasture is the main land cover in the catchment, followed by indigenous vegetation.

A variety of streams feed the lake. Of these, the Hamurana Stream has the greatest flow. Geothermal inputs flow via streams such as the Puarenga and Waiohewa Streams, and there are hot springs along the lake’s southern shore. There are two monitoring sites for this lake located north and south of Mokoia Island. Each has a maximum depth of 20m. The lake’s aquatic plant remains low but stable. The invasive condition has improved slightly because Egeria declined in Lake Rotorua in the late 1980s and has never recovered. Future water quality improvements in this lake will cause aquatic pest plant species to proliferate, increasing the risk of large weed strandings. Lake Rotorua contains three of the region’s worst aquatic pest plant species and poses a risk to neighbouring lakes that are free of these species. Internal phosphorus and nitrogen recycling between the sediment and water column contributes a significant proportion of the nutrient load to Lake Rotorua. This, combined with the relatively old age of inflowing nutrient-laden groundwater, means restoration of the lake isn’t likely to be achieved quickly. Restoration work on Lake Rotorua continues to ensure the lake meets its long-term water quality (TLI) targets. A range of intervention techniques have been implemented, including alum dosing of two tributary streams as a short-term measure to reduce phosphorus levels, rules designed to reduce nitrogen inputs from the catchment and sewage reticulation to reduce septic tank inputs.

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 Rotorua
    Year
    TLI history for Lake Rotorua 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 Rotorua
    Year
    LakeSPI history for Lake Rotorua 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.
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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 Rotorua

...retrieving sites.

No sites found.

Live Data

Disclaimer

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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