Trophic state index
Oligotrophic lakes have very little or no aquatic vegetation and the water is clear. They have low levels of nutrients. The water is suitable as drinking water. The bottom waters of such lakes typically have lots of oxygen; thus, such lakes often support many fish species. Lake trout, for example, need cold, oxygen rich water. The oxygen content is likely to be higher in deep lakes, because of their larger amount of dense cold water.