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Lake Rotoiti

Lake Rotoiti is the third-largest Rotorua Te Arawa lake and occupies part of the Haroharo Caldera. The lake deepens from west to east, changing from an average of 10m deep to a maximum of 125m northeast of Gisborne Point. The 123.7sq km catchment is mainly covered in indigenous vegetation (36.4 percent) and exotic forestry (46.2 percent). There has been a conversion of pastoral lands to forestry over the past 30 years.

There are numerous geothermal inputs to the lake, with the largest coming from the Tikitere geothermal field. Several small streams discharge to the lake in the eastern basin and a few warm streams discharge into the western basin, but the main input is from Lake Rotorua via the Ohau Channel into the western basin. Water passes through the channel at an average rate of 15cu m per second. Prior to the construction of the Ohau Channel diversion wall this water sometimes plunged into the eastern basin of Lake Rotoiti as an underflow. The flow is now effectively diverted directly to the outlet at Okere and on to the Kaituna River. The Ohau Channel diversion wall was completed in July 2008 and results in nutrient reduction to Lake Rotoiti (76 percent for phosphorus and up to 73 percent for nitrogen). The reticulation of sewage from the Okawa Bay community was completed in 2008 and may be one of the reasons for the water clarity improvements seen at Okawa Bay. Land management options continue to be developed around the lake with riparian plantings and fencing off of waterways from stock. Oxygenation and capping of the lake bed sediments could also result in improvements to the lake. Lake Rotoiti has three water quality monitoring sites - in the deep eastern basin, in the narrows between the two western basins and in Okawa Bay. An electronic cyano-bacteria health warning sign at Gisborne Point continues to provide lake users with up-to-date health warning information.

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 Rotoiti

    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 Rotoiti 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 Rotoiti

    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 Rotoiti data table
    Sample Date LakeSPI Status LakeSPI % Native Condition Index % Invasive Impact Index %
    LakeSPI information has been provided by NIWA.

Monitored sites on Lake Rotoiti

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No sites found.

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