Environment - Lake water quality by trophic state 2009–2013

Trophic level index: The lake trophic level index (TLI) indicates the health of a lake based on its degree of nutrient enrichment. The trophic states represent increasing nutrient enrichment, from a state of microtrophic (very good) to supertrophic (very poor).

Microtrophic (TLI < 2; very good) lakes are very clean and often have snow or glacial sources (eg Lake Pukaki in Canterbury)
Oligotrophic (TLI 2–3; good) lakes are clear and blue, with low concentrations of nutrients and algae (eg Lake Rotoma in Bay of Plenty)
Mesotrophic (TLI 3–4; average) lakes have moderate concentrations of nutrients and algae (eg Lake Rerewhakaaitu in Bay of Plenty)
Eutrophic (TLI 4–5; poor) lakes are murky, with high concentrations of nutrients and algae (eg Lake Rotoroa in Northland)
Supertrophic or hypertrophic (TLI > 5; very poor) lakes have extremely high concentrations of phosphorus and nitrogen, and are overly fertile; they are rarely suitable for recreation and lack habitats for desirable aquatic species (eg Lake Forsyth in Canterbury).

Figure.NZ calculated the count of lakes by tropic state to mirror the analysis undertaken for the Environmental Reporting Series (see http://stats.govt.nz/browse_for_stats/environment/environmental-reporting-series/environmental-indicators/Home/Fresh%20water/lake-water-quality.aspx Figure 1)

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