THE E.P.A currently uses the Carlson trophic state index (CTSI) as the index of the degree of eutrophication. CTSI consists of the concentration of three items of water quality parameters: Transparency(SD), Chlorophyll-a(Chl-a), Total Phosphate(TP), which are calculated to form an index value, and determine the eutrophication level of reservoir water quality. Carlson trophic state index (CTSI)=(﹝TSI(SD)+TSI(Chl-a)+TSI(TP))/3 SDTransparence；Chl-a：Chlorophyll-a；TP：Total Phosphate；TSI Exponent calculation method TSI(SD)=60-14.41 x ln(SD), The unit of SD(Transparence) is meter TSI(TP)=14.42 x ln(TP)+4.15, The unit of total phosphate is μg/L TSI(CHA)=9.81 x ln(CHA) +30.6, The unit of Chlorophyll-a is μg/L Note: ln is Natural logarithm. Carlson index (CTSI) Eutrophication level CTSI < 40 Oligotrophic 40 ≦ CTSI ≦ 50 Mesotrophic CTSI > 50 Eutrophic Eutrophication standards for single parameter index Class Total Phosphate (μg/L) Chlorophyll-a (μg/L) Transparence (m) Oligotrophic < 12 < 2.6 > 4 Mesotrophic 12 ~ 24 2.6 ~ 7.2 2 ~ 4 Eutrophic > 24 > 7.2 < 2