Lakes are natural resources, which have many effects on the land surrounding them, They support adjacent communities by providing water and regulating temperatures, helping to define the surrounding ecosystem, and serving as sources of drinking water as well as recreation. The prolonged presence of human activity in a watershed can disturb the physical and chemical cycles of the lake and its surrounding ecosystems (Henderson-Sellers and Markland 1987). Over time, lakes undergo a process called eutrophication, a natural aging process during which the nutrient levels increase and dissolved oxygen levels decrease (Smith and Smith 1998). As the lake ages or becomes more eutrophic, organic material gradually collects in the lake basin. For a period of time, the increased organic matter raises the nutrient level in the lake and causes higher productivity. As the lake becomes more eutrophic, dissolved oxygen (DO) levels fall because of the high levels of organic material decomposing in the water. Organisms that cannot live under low dissolved oxygen levels begin to die. Over time, as DO levels continue to drop the diversity and overall health of the lake decrease until only a few highly tolerant species remain (Henderson-Sellers and Markland 1987).
Problems in Environmental Science course (Biology 493), Colby College and Colby Environmental Assessment Team, Colby College, "Land Use Patterns In Relation To Lake Water Quality In The Great Pond Watershed" (1998). Colby College Watershed Study: Great Pond (2012, 2010, 1998). Paper 1.