Factsheet: Lake SPI

Lake Submerged Plant Indicators (Lake SPI) is a method of characterising the ecological health of lakes based on the amount of native and invasive plants growing in them.  Presented as a percentage, higher Lake SPI scores are associated with the better water quality.

The Lake SPI displayed on LAWA is provided by NIWA using data collected by councils, Department of Conservation and NIWA

How is Lake SPI measured?

Councils, the Department of Conservation and NIWA are all involved in collecting data used to calculate Lake SPI. These agencies carry out surveys of the plants growing under the surface of lakes using scuba divers. The data collected on these surveys is used to determine the:

  • Native Condition Index: the percentage of native vegetation within a lake. A high Native Condition Index is desirable.
  • Invasive Impact Index: the percentage of invasive weeds within a lake. A high Invasive Impact is undesirable.

 The native condition and invasive impact indices are used together to generate a LakeSPI Index, which provides an overall indicator of lake ecological condition.

Lake SPI


What do the Lake SPI numbers mean?

The Lake SPI percentage gives an indication of ecological health, the higher the Lake SPI percentage, the better the ecological health of the lake.  Each range of percentages translates into a scientific description as explained in the table below:




75%-100% Excellent ecological health
50%-75% High ecological health
20%-50% Moderate ecological health  
0%-20% Poor ecological health  
0% Non-vegetated (no plants present)  












Does Lake SPI change over time?

The ecological health of a lake can change over time as the proportion of native and/or invasive plants changes.  You can see the historical Lake SPI for a lake by clicking on the “show more information” button. 

SPI History

Find out more:

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Lake SPI data on LAWA is provided by NIWA. You can find out more about Lake SPI and how it is measured by visiting the NIWA Lake SPI site.