What makes a Lake?

Lake Variability and Desciptions
(North American Lake Management Society) http://www.nalms.org/

Each lake has qualities which make it unique, much like people with distinct personalities.  Lakes vary based on physical characteristics, such as size, depth configuration, chemical characteristics (such as soft versus hard water), water clarity, or the types of plant and animal life present.  For example, hard water lakes have higher levels of dissolved minerals such as calcium, iron and magnesium than soft water lakes.  Some lakes, expecially those near acidic wetlands like bogs, are stained with tannic acid that leaches from surrounding vegetation.  The water in these "tannin lakes" may range in color from a dark brown "coffee" color to light brown. 

Natural lakes in Wisconsin frequently are classified by the source of water supply.  Based on water source and outflows, four categories of lakes have been identified in the publication:

1.  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 owing one-half of their maximum depth to a dam are considered to be artifical lake sor impoundments.

2.  Seepage lakes - These lakes do not have an inlet or an outlet, and only occasionally overflow.  As landlocked waterbodies, 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. 

3.  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 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.  

4.  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.