Rating of the condition of a lake on the scale of oligotrophic-mesotrophic-eutrophic (see definition of these terms).

The descriptive phase of a lake: oligotrophic, mesotrophic, eutrophic or somewhere in between. (Flathead Lake currently is described as oligomesotrophic).

A term used to describe the productivity of a lake ecosystem classifying it as one of three increasing categories based on algal biomass: oligotrophic, mesotrophic, or eutrophic. Trophic state indicators are calculated on the basis of the relationships derived between total phosphorus, chlorophyll-a or secchi transparency measurements and algal biovolume in a study conducted by Robert Carlson in 1977.