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Lake Waahi

West of Huntly in a predominantly pastoral catchment, Lake Waahi is the third largest lake in the lower Waikato. It receives water from a range of sources and discharges to the Waikato River via Waahi Stream.

Lake Waahi has been considerably affected by nutrients and sediment, ongoing issues related to its modification, riparian management, and exotic and invasive fish and plant species. Its level has been substantially reduced, and many of the surrounding wetlands converted to pasture for farming.

The lake has played a significant role in commercial coal mining operations since 1876, both as a water source, and a receiving environment for discharges. Coal mining has contributed large quantities of sediment to the lake, altering the lake’s colour, clarity and chemistry. Coal mining was reportedly responsible for up to 90 per cent of the sediment entering the lake at times.

Waikato Regional Council has monitored the water quality of Lake Waahi since September 1995, and installed a monitoring buoy in 2014 to collect real-time information. Recent monitoring results indicate the lake has low water clarity, high nutrient levels, and high phytoplankton density. Blue-green algae have been abundant in recent years.

Lake Waahi is identified as a priority 1 waterbody for stock exclusion in the Waikato Regional Plan. Planting and fencing have been undertaken as part of a collaborative project between Solid Energy, Waikato Regional Council, and private landowners, with additional funding support from WCEET.

Waikato Regional Council has contributed to the costs of around 9km of fencing at Lake Waahi. In 2011, the Waikato River Clean Up Trust provided around $600,000 to Waikato-Tainui, Waahi Whaanui Trust and Genesis Energy for a holistic restoration programme at Lake Waahi, involving riparian management/wetland enhancement, establishment of a community nursery, and control and management of koi carp.

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 Waahi
    TLI history for Lake Waahi 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 Waahi
    LakeSPI history for Lake Waahi 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 Waahi

...retrieving sites.

No sites found.

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