Lake Type: How Does Water Get Into Your Lake?

Inflows to a lake come from precipitation, runoff, groundwater flow, and in some cases surface flow (streams and rivers). Outflows from a lake go to evaporation, and in some cases groundwater or surface flow.

Seepage Lakes - These lakes have no surface water inflows or outflows. Most water comes from groundwater flow. A natural lake fed by precipitation, limited runoff and groundwater. It does not have a stream outlet.

Groundwater Drainage Lakes - have no surface water inflows but do have surface water outflows. Most water comes from groundwater flow. A natural lake fed by groundwater, precipitation and limited runoff. It has a stream outlet.

Drainage Lakes - have surface water inflows and outflows; groundwater flow plays a minor role. A lake fed by streams, groundwater, precipitation and runoff and drained by a stream.

Impoundments are manmade lakes, and often act like drainage lakes. A manmade lake created by damming a stream. An impoundment is also drained by a stream.

Trophic state is another indicator of water quality. Lakes can be divided into three categories based on trophic state-oligotrophic, mesotrophic, and eutrophic. These categories reflect a lake's nutrient and clarity levels.

Lakes can be divided into three categories (trophic states) based on a lake's nutrient and clarity levels:

Oligotrophic Lakes are generally clear, deep and free of weeds 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 small fish.

Eutrophic Lakes are high in nutrients and support a large biomass (all the plants and animals living in a lake). 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.

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.

A natural aging process occurs in all lakes, causing them to change from oligotrophic to eutrophic over time, and eventually to fill in. People can accelerate the eutrophication process by allowing nutrients from agriculture, lawn fertilizers, streets, septic systems, and urban storm drains to enter lakes.

In nutrient-poor areas, the aging process may lead instead to dystrophic and bog lakes which are highly colored, acid, and not as productive as eutrophic lakes.

Researchers use various methods to calculate the trophic state of lakes. Common characteristics used to make the determination are:

Total phosphorus concentration (important for algae growth)

Chlorophyll a concentration (a measure of the amount of algae present)

Secchi disc readings (an indicator of water clarity).