They are usually either weedy or subject to frequent algae blooms, or both. Eutrophic lakes often support large fish populations, but are also susceptible to oxygen depletion. Small, shallow, eutrophic lakes are especially vulnerable to winterkill which can reduce the number and variety of fish. Rough fish are commonly found in eutrophic lakes. Mesotrophic lakes lie between the oligotrophic and eutrophic stages.
Researchers use various methods to calculate the trophic state of lakes.