A lake can be put into one of three possible classes: "oligotrophic", "mesotrophic" or "eutrophic". Lakes with extreme trophic indices can also be called "hyperoligotrophic" or "hypereutrophic". Each trophic class has different types of fish and other organisms which live in them. If there is too much algal biomass in a lake or pond, then many fish can die as the decomposing biomass takes the oxygen from the water.