Buying a lake cabin – know your lake classification

How does water get into your lake?

Gordon Dam

Hydrologists divide lakes into two main types: drainage and seepage.  Drainage lakes have an inlet and outlet; they’re part of system that “drains” a watershed.  They’re less affected by drought.  Seepage lakes get their water from springs, and from water that just “seeps” into the lake from the adjacent water table.  Some are totally unaffected by drought.

The following lakes classification, further divided into five main lake types, is courtesy of the Wisconsin Association of Lakes Water can enter lakes from a variety of sources including groundwater, runoff from the watershed, surface waters (like streams and rivers) flowing into the lake, and direct precipitation into the lake. Water leaves lakes through groundwater or surface water flow and evaporation. The water quality of a lake and species of fish present are significantly influenced by the lake type.

Seepage lakes – Seepage lakes do not have an inlet or an outlet, and only occasionally overflow. Landlocked bodies, the principal source of water is precipitation or runoff, supplemented by groundwater from the immediate drainage area. Since seepage lakes commonly reflect groundwater levels and rainfall patterns, water levels may fluctuate seasonally. Seepage lakes are the most common lake type in Wisconsin.

Seepage lakes frequently have a less diverse fishery because they are not influenced by streams. Seepage lakes also have a smaller drainage area, which may help to account for lower nutrient levels.

Spring lakes – These lakes have no inlet, but do have an outlet. The primary source of water for spring lakes is groundwater flowing into the bottom of the lake from inside and outside the immediate surface drainage area. Spring lakes are the headwaters of many streams and are a fairly common type of lake in northern Wisconsin.

Groundwater drained lakes – These lakes have no inlet, but like spring lakes, have a continuously flowing outlet. Drained lakes are not groundwater-fed. Their primary source of water is from precipitation and direct drainage from the surrounding land.

Frequently, the water levels in drained lakes will fluctuate depending on the supply of water. Under severe conditions, the outlets from drained lakes may become intermittent. Drained lakes are the least common lake type found in Wisconsin.

Drainage lakes – These lakes have both an inlet and outlet where the main water source is stream drainage. Most major rivers in Wisconsin have drainage lakes along their course. Drainage lakes support fish populations which are not necessarily identical to the streams connected to them. Drainage lakes usually have higher nutrient levels than many natural seepage or spring lakes.

Impoundments – Artificial lakes are human-made bodies of water referred to as impoundments. A lake is considered an impoundment if one-half or more of its maximum depth results from a dam or other type of control structure. An impoundment is considered a drainage lake since it has an inlet and outlet with its principal water source coming from stream drainage. In Wisconsin, this body of water is commonly known as a flowage, and can often be quite large lakes.

Impoundments may support fish populations which are not necessarily identical to the streams connected to them. Impoundments usually have higher nutrient levels than many natural seepage or spring lakes.

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