Reflecting on Lakes

How protecting your watershed can improve your lake

A high quality lake, valued for recreation and aesthetic appeal, can benefit all watershed residents (and nonresidents alike) by providing a healthy place to play and/or enjoy a quiet sunset. In other words, a high quality lake improves the quality of the community’s life. Property values, not only on the lakeshore, but throughout the watershed community, can benefit from a desirable lake.

Six keys to protecting lakes

  1. Valuing high quality lakes
  2. Understanding the link between the lake and its watershed
  3. Understanding in-lake processes
  4. Recognizing and preventing threats to lake quality
  5. Forming partnerships with lake-watershed members
  6. Knowing where to go for help

A lake is the reflection of its watershed (the land that drains — eventually — into it) and the everyday actions that take place on the watershed. The importance of the relationship between a lake and its watershed cannot be over emphasized when protecting, managing or restoring a lake. The lake-watershed “system” is a functioning unit with interacting biological, physical, chemical and human components.

If a lake suffers from problems such as extensive weed growth or algal scum, fish kills, or filling in with sediments, often the cause of the problem can be linked to a source or sources within the watershed.

The characteristics of lake-watershed interaction depend on a number of variables. Some variables include the ratio of drainage area to lake area, how the land is used, the climate, soils and geography, as well as existing conservation measures.

Sizes and shapes

The origin of a lake often determines the size and other characteristics of the lake. “Man-made” lakes, often referred to as impoundments or reservoirs, are those that were formed by damming a drainageway, stream or river. Man-made lakes can range in size and shape from the smallest farm pond to huge “run-of the-river” reservoirs such as Lake Mead formed by the Hoover Dam.

Lake-watershed size relationship

If a lake is small relative to its watershed, the potential is greater for the lake to fill in with sediment or be affected by nutrients tied to the soil particles, than a large lake with a relatively small watershed.

Climate and soils

Lakes in areas with more rainfall and steep, erosive, nutrient-rich soils will have greater potential for algae blooms and plant growth than those in dry climates with infertile soils.


In general, the greater the slope of the land in the lake’s watershed, the greater the potential of pollutants reaching the lake.

Lake productivity stages

In-lake factors combined with the lake-watershed relationship, determine how “productive” a lake will be. The biological productivity of a lake is based on the availability of plant nutrients and is referred to as the lakes “trophic” condition. Extremely high or low productivity usually limits aquatic life. High productivity leads to lots of algae and other aquatic plants. Low productivity leads to very little aquatic life.

The trophic condition of lakes ranges from the least productive (oligotrophic) to moderately productive (mesotrophic) to highly productive (eutrophic). Hypereutrophic lakes are the most productive of all. The process of moving from an oligotrophic state to a eutrophic state, is a natural process that can take thousands of years, as sediment from the watershed carries nutrients slowly into the lake.

However, where human activity has affected a watershed, lake productivity can dramatically increase over a relatively shorter period of time. This type of eutrophication–as a result of watershed disturbance by humans — is known as “cultural” eutrophication.

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