SummaryTrophic state index is a measure of how eutrophic conditions are in a water-body. Excess algal growth can indicate eutrophic conditions and is the basis of the index. General Information about this IndicatorWhat is it?: This indicator was developed primarily for lakes, but can be used for embayed waters, and is a measure of micro-algal growth. The higher the value, the higher the concentration of algal cells, which can indicate eutrophic conditions.