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What Makes a Lake?

Wisconsin -- the word is thought to refer to a running river, which makes sense because lakes and rivers make up a large part of Wisconsin's natural resources. Wisconsin has: lake scene

  • the third largest concentration of fresh water glacial lakes on the planet
  • more than 84,000 miles of rivers and streams
  • more than 15,000 inland lakes
  • about 1,751 square miles of Great Lakes estuaries and bays, along 1,017 miles of Great Lakes shoreline
  • approximately 5.3 million acres of wetlands

Wisconsin's lakes and waterways are important, not only for business, but also recreation. From the shores of Lakes Michigan and Superior to the Mississippi River, Wisconsin has an incredible wealth and variety of water resources: trout streams and floodplain forests; streams and creeks of northern forests; and inland lakes and wetlands created by ice-age glaciers. Maintaining the quality of these waters and the beauty of the shorelands is important for both people and wildlife.

What makes a lake? A lake is a body of standing water (not moving that is). This can include natural lakes (formed by glaciers, oxbows in rivers, or other natural processes) and impoundments, or human made lakes, such as reservoirs and farm ponds. Lakes are a critical part of the environment, serving as the collection point for all of the water that falls in the area that travels down through what's called the watershed. The watershed is made up of all the streams and rivers that flow into a particular lake.

Lakes and their nearby wetlands are important to people and ecosystems because they:

  • Provide critical habitat for fish, wildlife, and tiny water critters
  • Provide a place for sediments to settle and spread out
  • Control floods
  • Recharge the groundwater
  • Provide a recreational area
  • Serve as a place of beauty and inspiration for residents and visitors

Lakes get old naturally over time, filling in with sediments, nutrients, plants, and algae. They also become shallower. This aging process usually takes hundreds to thousands of years. With human influence, lakes can fill in faster--sometimes in only decades. lake scene

Inside the lake environment there are physical, chemical, and biological processes that determine the type and number of plants, animals, and tiny organisms that are able to live there. One such process is called "stratification." During summer, the lake becomes layered with warm water at the surface and cooler water sinking to the bottom. You might notice this when you're treading water and your feet are hanging lower in the lake. Stratification can change the oxygen content, light penetration, and photosynthesis in a lake, all of which affect the entire lake ecosystem. In the fall, the top layer cools and the lake is all one temperature. Winds mix the water and the lake "turns," so that winter waters are warmer near the bottom where fish spend the winter, and colder water is near the surface where the lake freezes. In the spring, the lake "turns" again and it begins all over.

When looking out at a lake, you might not think that much is going on underneath the surface, but a lot is happening with lake chemistry, stratification, wind mixing, and the aquatic organisms that live there. By learning more about lakes, you can help protect them and better understand the processes in and around the lake. Get involved in protecting the lake nearest you. You'll be helping wildlife and your community.

Back to Lakes are Great

*Adapted from the Adopt-A-Lake Manual, 1999.



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