Water Pollution in Streams and Rivers

Agricultural pollution (nutrients, sediments) is very visible here where a river enters a coastal area. Mangiwau/Moment Open/Getty

About one third of the nation’s rivers and streams are routinely assessed for water quality by the Environmental Protection Agency (EPA). Out of the 1 million miles of streams examined, over half had waters considered impaired. A stream is categorized as impaired when it cannot fulfill at least one of its uses, which include a variety of functions like fish protection & propagation, recreation, and public water supply. Here are the 3 most significant causes of stream and river pollution, in order of importance:

  1. Bacteria. Contamination of water by certain types of bacteria is certainly a human health issue, as we are particularly susceptible to disease-causing gut bacteria. Beach safety is routinely monitored through coliform bacteria counts. Coliform bacteria inhabit the gut of animals, and are a good indicator of fecal contamination. When there is a high count of coliform bacteria, the odds are high that the water also contains microorganism that can make us sick. Gut bacteria contamination can come from municipal sewage treatment plants that overflow during heavy rain events, or from leaky septic tank systems. Abundant animals near the water, for example ducks, geese, gulls, or cattle, can also result in bacteria contamination.
  2. Sediment.  Fine-grained particles like silt and clay may occur naturally in the environment but when they enter streams in large quantity, they become a serious pollution problem. Sediments come from the many ways soil can be eroded on land and carried into streams. Common causes of erosion are road construction, building construction, deforestation, and agricultural activities. Anytime there is a significant removal of the natural vegetation, the potential for erosion exists. In the United States, vast farm fields are left barren much of the year, and as a result rain and melting snow wash away soil into streams and rivers. In streams, sediments block sunlight and thus impede the growth of aquatic plants. Silt can smother the gravel beds necessary for fish to lay eggs. Sediments that remain suspended in the water are eventually carried off into coastal zones, where they affect marine life.
  1. Nutrients. Nutrient pollution occurs when excess nitrogen and phosphorus make their way into a stream or river. These elements are then picked up by algae, allowing them to grow rapidly to the detriment of the aquatic ecosystem. Overabundant algae blooms can lead to toxin build-up, oxygen level drops, fish kills, and poor conditions for recreation. Nutrient pollution and the subsequent algae blooms are to blame for Toledo’s drinking water shortage in the summer of 2014. Nitrogen and phosphorus pollution comes from inefficient sewage treatment systems, and from a common practice in large-scale farms: synthetic fertilizers are often applied in fields at greater concentrations than the crops can use, and the excess winds up in streams. Concentrated livestock operations (for example, dairy farms or cattle feedlots) lead to large accumulations of manure, with nutrient runoff difficult to manage.

Not surprisingly, the most widespread source of stream pollution is reported by the EPA to be agriculture. Other important sources of problems are atmospheric deposition (usually air pollution that is brought into streams with rainfall), and the presence of dams, reservoirs, stream channels, and other engineered structures.


EPA. 2015. Water Quality Assessment and TMDL Information. National Summary of State Information.

Food and Agriculture Organization of the United Nations. Control of Water Pollution from Agriculture.


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