When a lake or surface water body or groundwater gets too many nutrients added to it, then certain organisms in the water grow rapidly and cause damage to the water. Common nutrients include phosphates and nitrates, which occur naturally but also are added to the environment by human activities.  When the phosphates and nitrates enter the water system in excessive amounts, they promote the growth of algae that absorbs the oxygen and deprives fish and other organisms of the oxygen they need to survive.  This depletion of oxygen in the water is called hypoxia.  A symptom of the condition is the presence of algae blooms, and it can reduce the biodiversity of the ecosystem where it occurs.

Eutrophication can occur naturally but it is more commonly the result of human activities.  Activities that promote eutrophication include fertilisers from farming, lawns and gardens, sewage from treatment plants or faulty septic systems, stormwater runoff from developed land, and even washing with soap in or near the water course.

As fertilizers used in farming, often in excessive applications, and discharge of raw sewage are the most frequent causes, laws and regulations controlling these sources have been effective in reducing the impacts.  The construction and improvement of wastewater treatment plants to reduce or eliminate raw sewage are expensive but necessary and effective.  The European Union Nitrates Directive is intended to reduce the negative impacts from the use of fertilisers in farming but it has met with opposition from the farming community.

Some further ideas to explore on Eutrophication:

Identify a lake or river or stream or other water body near you and research its current condition.  Determine if it is subject to eutrophication, currently or periodically or in the past.  Or find the nearest water body that is suffering from some degree of eutrophication.

Determine the cause and the sources of any human activities that are negatively impacting the condition of the water.

Is there anything you can do to help stop whatever is harming the water?


UK Water Pollution Guide, “Eutrophication,”


European Environment Agency, “Eutrophication,”


United States Geological Survey, “Eutrophication,” toxics.usgs.gov/definitions/eutrophication.html

Environmental Protection Agency (Ireland), Eutrophication from Agricultural Sources – Integrated Report ERTDI Report 81 (Carton et al.)


See Northern Ireland State of the Seas in the Reports section of the current (March) issue of irish environment

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