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Monitoring of overall lake health - measuring the Trophic Level Index

by Julia.Charity, 4 months ago

What is the Trophic Level Index?

The Trophic Level Index (TLI) is used to give an overall picture of the health of New Zealand lakes. 

Each lake is assigned a number between 1 and 7.  1 being the highest ranking for the best water quality and 7 being the lowest.  

The Trophic Level Index measures four important factors:

  1. Water clarity
  2. Chlorophyll content
  3. Total phosphorus
  4. Total nitrogen

Why is measuring TLI important?

The lower the number, the better the water quality in the lake, so the TLI is an important indicator of how healthy the lake is. 

Conversely, the higher the value, the greater the nutrients and fertility of the water, which encourages growth, including algal blooms.

Want more information about TLI? Check out the factsheet here

What is the TLI for Lake Hayes?

LAWA (Land, Air, Water Aotearoa) has been measuring the Trophic Lake Index for Lake Hayes since 2005. Here's what that data looks like: 


Here's some important information about what the different coloured data points mean. 

With a TLI in the range 4 - 5, Lake Hayes is currently rated as having poor water quality. LAWA have scored this lake as Eutrophic.

Eutrophic lakes have an abundance of nutrients that support a dense growth of algae and other organisms. When these die, their decay reduces oxygen in the shallow waters in summer. This means Lake Hayes is likely to be green and murky, with higher amounts of nutrients and algae in some areas of the lake. 

You can also go to the LAWA website for Lake Hayes to view the data.

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