State of the Environment freshwater monitoring programme
Lakes Water Quality Programme
On this page:
- What is the Lakes Water Quality Programme?
- How does it work?
- What is the Trophic Level Index (TLI)?
- What are the trophic states?
What is the Lakes Water Quality Programme?
The water quality of any lake is known as its trophic state. It is very closely linked to the land use and the amount of land disturbance in the surrounding catchment. Commencing in 1998, our Lakes Water Quality Programme is designed to measure the trophic state of a lake over time so that any short-term changes, and long-term trends, in the quality of the water can be detected.
Our current programme began in 1998.
How does it work?
The water quality is checked once every two months at the seven largest natural lakes in the Auckland region, see the map below.
Detailed results are shown in annual reports that are available from our Technical Publications.
Monitoring of the water quality is consistent with the protocol for monitoring lake trophic levels and assessing trends in trophic state. This was developed by the Ministry of the Environment in 2002.
What is the Trophic Level Index (TLI)?
This protocol enables us to measure the quality of any lake water using four key water quality indicators:
- Chlorophyl a
- Visual clarity
- Total Phosphorus
- Total Nitrogen
The results for each water indicator are mathematically processed and then combined to produce an overall Trophic Level Index (TLI) rating for the lake.
The TLI rating shows the trophic state of the lake; e.g, a TLI rating of 5.2 tells us that the lake water is supertrophic.
Trophic State | ||||||
| Microptrophic | Oligotrophic | Mesotrophic | Eutrophic | Supertrophic | Hypertrophic | |
| Trophic Level Index (TLI) Rating | <2.0 | 2.0 - 3.0 | 3.0 - 4.0 | 4.0 - 5.0 | 5.0 - 6. 0 | 6.0 - 7.0 |
What are the trophic states?
The trophic state is determined from the Trophic Level Index (TLI) rating for the lake. It shows the state of the lake water.
Trophic State | |||||
| Microptrophic | Oligotrophic | Mesotrophic | Eutrophic | Supertrophic | Hypertrophic |
| These lakes are very clean and often have snow or glacial sources. | These lakes are clear and blue, with low levels of nutrients and algae. | These lakes have moderate levels of nutrients and algae. | These lakes are green and murky, with higher amounts of nutrients and algae. | These lakes are fertile and saturated in phosphorus and nitrogen, and have very high algae growth and blooms during calm, sunny periods. | These lakes are highly fertile and super-saturated in nutrients (phosphorus and nitrogen). They are rarely suitable for recreation and habitat for desirable aquatic species is limited. |
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