Causes & Effects of Eutrophication


In the natural course of events, lakes and other bodies of freshwater receive nutrients like phosphorus and nitrogen. The gradual accumulation of these nutrients involves a process called eutrophication. As the lake ages, the nutrients build up with various effects. The process speeds up with cultural eutrophication, which involves the effects of man on the freshwater body.


  • The basic cause of eutrophication is the accumulation of nutrients in a body of water. This process is part of the normal course of events for lakes. A young lake contains pure water, which over a long period of time gains nutrients primarily from runoff of organic materials. These materials build up as more nutrients enter the system than are required for algae and other organisms. As the lake ages, the excess nutrients cause problems.


  • Fertilizers contain nitrogen and phosphorus, which are essential nutrients for enriching the soil with the goal of increased agricultural production. These products continue to be used in larger and larger quantities. Nitrogen and phosphorus enter lakes and streams through several means. They include accidental discharge and runoff during rain and other water-related conditions. Use more fertilizer and the chances of some of it ending up in lakes increases. Fertilizers represent the main reason for cultural eutrophication, according to the National Oceanic and Atmospheric Administration (NOAA).

Algal Blooms

  • One of eutrophication's effects is algal blooms that result from excessive deposits of nutrients. The algae feeds on the nutrients and experiences rapid growth. As the algae grows and covers the lake or other waterway, sunlight is prevented from reaching the water. Eventually, the algae depletes the nutrients and the algae dies off. The decaying algae depletes the oxygen in the water, which impacts all living organisms in the water, many times leading to their demise.

Aquatic Life

  • Eutrophication of lakes and other bodies of water causes shifts in the types of aquatic life that survive. Many fish species disappear due to insufficient oxygen supplies. Carp represents a species of fish that survives in a low-oxygen environment. Advanced eutrophication kills all aquatic life and, with no more oxygen to support life, the body of water becomes dead.


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