Water pollution has many sources and characteristics. Humans and other organisms produce bodily wastes which enter rivers, lakes, oceans, and other surface waters; in high concentrations these wastes result in bacterial contamination and excessive nutrient loading. Industries discharge a variety of toxic compounds and heavy metals, and industrial process wastewater may also be too hot or too low in dissolved oxygen to support life. Silt-bearing runoff from construction sites and farms can inhibit the penetration of sunlight through the water column, and hampers water organisms in their search for food.

Causes

The causes of water pollution can be divided into two groups: anthropogenic sources of pollution are those due to human choices, and natural sources are those resulting from forces intrinsic to the environment. Anthropogenic sources include:

• discharge of poorly-treated or untreated sewage;
• runoff from construction sites, farms, or paved and other impervious surfaces;
• discharge of contaminated and/or heated water used on industrial processes
• acid rain caused by industrial discharge of sulphur dioxide (by burning high-sulfur fossil fuels)

Natural sources include:

• seasonal turnover of lakes and embayments;
• siltation due to floods;
• eutrophication of lakes due to seasonal changes
• acid rain caused by natural volcanic discharges
• acid pollution of rivers and lakes by runoff from naturally acid soils
• carbon dioxide discharges and runoff, volcanic or mineral

Contaminants

Contaminants may include organic and inorganic substances. Organic water pollutants include:

• bacteria, as from sewage or livestock operations;
• food processing waste;
• tree and brush debris from logging operations

Inorganic pollutants include:

• metals;
• acid mine drainage;
• silt in stormwater runoff from cleared land
• acid rain caused by industrial or volcanic discharges
• acid pollution of lakes by runoff from acid soils
• carbon dioxide discharges and runoff, volcanic or mineral

Further reading

Sources

U.S. Environmental Protection Agency Homepage, http://www.epa.gov/

Kentucky Division of Water Homepage, http://water.ky.gov/

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