Lakes can be classified into three categories or trophic states—oligotrophic, mesotrophic, and eutrophic. A natural aging process occurs in all lakes, trophic states are a snapshot of where a lake is in the aging process. The trophic state indicates the amount of nutrients and productivity (the level of plant and animal life the lake can support) and accumulation of sediments.
Over time, lakes change from oligotrophic, to mesotrophic, to eutrophic, and eventually, lakes fill in with sediment. As lakes age and the trophic state changes, the species that can survive in the lake shift. Generally, the more nutrients (food) present means the lake can support a richer array of species and more complex ecosystem.
Oligotrophic lakes are generally clear, deep and free of aquatic plants or large algae blooms. Though beautiful, they are low in nutrients and do not support large fish populations. However, oligotrophic lakes often develop a food chain capable of sustaining a very desirable fishery of large game fish.
Mesotrophic lakes lie between the oligotrophic and eutrophic stages. Devoid of oxygen in late summer, their hypolimnions limit cold water fish and cause phosphorus cycling from sediments.
Eutrophic lakes are the most nutrient rich lakes, and support a large and diverse volume of plants and animals. They are usually either full of aquatic plants 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.
People can accelerate the eutrophication process by allowing nutrients from agriculture, lawn fertilizers, streets, septic systems, and urban storm drains to enter lakes.
