Pollution in Waterways

Pesticides, fertilizers, and animal waste from the agriculture industry are contaminating our lakes, waterways, and oceans. We’re also dumping over 180 million tons of toxic chemicals and other pollutants from industrial and mining practices into the world’s lakes, rivers, and oceans every year.

Rain can wash fertilizers, pesticides, and contaminated soil into rivers and streams, where it creates excessive amounts of nitrogen and phosphorous in the water. This excess of nutrients stimulates the growth of plants in lakes, taking up additional oxygen from the water and eventually killing organisms, insects and other aquatic life.

Pollution due to excess nutrients in freshwater or saltwater also results in algal blooms, which are a thick sludge or discoloring that covers the surface of a body of water. These toxic blooms pose a threat by depriving the water of oxygen, which is essential to the survival of aquatic species. A lack of sufficient oxygen kills off aquatic life and plants, resulting in dead zones and threatening the survival of the ecosystem. Land animals, birds, and humans can also be harmed by the contaminated water, or by consuming fish or shellfish that lived in contaminated water.

Animal Agriculture

Animal waste from factory farming contributes to water pollution when the large, open-air lagoons that house wastewater from the farms leak and contaminate local water supplies, or when runoff from the farms makes its way into nearby lakes and waterways. But it’s not only farms that contribute to waste; slaughterhouses are also to blame, with facilities in the U.S. being responsible for 55 million pounds of pollutants being into waterways each year.

Like pollution from pesticides and fertilizers, animal waste can contribute to algal blooms by introducing dangerous levels of ammonia, nitrogen and phosphorus into lakes and waterways. Animal waste from factory farms also contains hormones which, when introduced into water systems, can cause reproductive problems in fish.

As technology improves, scientists are able to detect more pollutants, and at smaller concentrations, in Earth’s freshwater bodies. Containing traces of contaminants ranging from birth control pills and sunscreen to pesticides and petroleum, our planet’s lakes, rivers, streams, and groundwater are often a chemical cocktail.

Beyond synthetic pollution, freshwater is also the end point for biological waste, in the form of human sewage, animal excrement, and rainwater runoff flavored by nutrient-rich fertilizers from yards and farms. These nutrients find their way through river systems into seas, sometimes creating coastal ocean zones void of oxygen—and therefore aquatic life—and making the connection between land and sea painfully obvious. When you dump paint down the drain, it often ends up in the ocean, via freshwater systems.

In some of the countries in developed world, regulation has restricted industry and agricultural operations from pouring pollutants into lakes, streams, and rivers. Technology has also offered a solution in the form of expensive filtration and treatment plants that make our drinking water safe to consume. Some cities are even promoting “green” infrastructure, such as green roofs and rain gardens, as a way to naturally filter out pollutants. But you may find a different picture in parts of the developing world, where there is less infrastructure—politically, economically, and technically—to deal with the barrage of pollution threats facing freshwater and all of the species that rely on it.

Water pollution occurs when a body of water is adversely affected due to the addition of large amounts of materials to the water. The sources of water pollution are categorized as being a point source or a non-source point of pollution. Point sources of pollution occur when the polluting substance is emitted directly into the waterway. A pipe spewing toxic chemicals directly into a river is an example. A non-point source occurs when there is runoff of pollutants into a waterway, for instance when fertilizer from a field is carried into a stream by surface runoff.

Types of Water Pollution

Toxic Substance — A toxic substance is a chemical pollutant that is not a naturally occurring substance in aquatic ecosystems. The greatest contributors to toxic pollution are herbicides, pesticides and industrial compounds.

Organic Substance — Organic pollution occurs when an excess of organic matter, such as manure or sewage, enters the water. When organic matter increases in a pond, the number of decomposers will increase. These decomposers grow rapidly and use a great deal of oxygen during their growth. This leads to a depletion of oxygen as the decomposition process occurs. A lack of oxygen can kill aquatic organisms. As the aquatic organisms die, they are broken down by decomposers which leads to further depletion of the oxygen levels.

A type of organic pollution can occur when inorganic pollutants such as nitrogen and phosphates accumulate in aquatic ecosystems. High levels of these nutrients cause an overgrowth of plants and algae. As the plants and algae die, they become organic material in the water. The enormous decay of this plant matter, in turn, lowers the oxygen level. The process of rapid plant growth followed by increased activity by decomposers and a depletion of the oxygen level is called eutrophication.

Thermal Pollution — Thermal pollution can occur when water is used as a coolant near a power or industrial plant and then is returned to the aquatic environment at a higher temperature than it was originally. Thermal pollution can lead to a decrease in the dissolved oxygen level in the water while also increasing the biological demand of aquatic organisms for oxygen.

Ecological Pollution — Ecological pollution takes place when chemical pollution, organic pollution or thermal pollution are caused by nature rather than by human activity. An example of ecological pollution would be an increased rate of siltation of a waterway after a landslide which would increase the amount of sediments in runoff water. Another example would be when a large animal, such as a deer, drowns in a flood and a large amount of organic material is added to the water as a result. Major geological events such as a volcano eruption might also be sources of ecological pollution.

Specific Sources of Water Pollution


– Farms often use large amounts of herbicides and pesticides, both of which are toxic pollutants. These substances are particularly dangerous to life in rivers, streams and lakes, where toxic substances can build up over a period of time.

– Farms also frequently use large amounts of chemical fertilizers that are washed into the waterways and damage the water supply and the life within it. Fertilizers can increase the amounts of nitrates and phosphates in the water, which can lead to the process of eutrophication.

– Allowing livestock to graze near water sources often results in organic waste products being washed into the waterways. This sudden introduction of organic material increases the amount of nitrogen in the water, and can also lead to eutrophication.

– Four hundred million tons of soil are carried by the Mississippi River to the Gulf of Mexico each year. A great deal of this siltation is due to runoff from the exposed soil of agricultural fields. Excessive amounts of sediment in waterways can block sunlight, preventing aquatic plants from photosynthesizing, and can suffocate fish by clogging their gills.


– Clearing of land can lead to erosion of soil into the river.

– Waste and sewage generated by industry can get into the water supply, introducing large organic pollutants into the ecosystem.

– Many industrial and power plants use rivers, streams and lakes to dispose of waste heat. The resulting hot water can cause thermal pollution. Thermal pollution can have a disastrous effect on life in an aquatic ecosystem as temperature increases/decreases the amount of oxygen in the water, thereby reducing the number of animals that can survive there.

– Water can become contaminated with toxic or radioactive materials from industry, mine sites and abandoned hazardous waste sites.

– Acid precipitation is caused when the burning of fossil fuels emits sulfur dioxide into the atmosphere. The sulfur dioxide reacts with the water in the atmosphere, creating rainfall which contains sulfuric acid. As acid precipitation falls into lakes, streams and ponds it can lower the overall pH of the waterway, killing vital plant life, thereby affecting the whole food chain. It can also leach heavy metals from the soil into the water, killing fish and other aquatic organisms. Because of this, air pollution is potentially one of the most threatening forms of pollution to aquatic ecosystems.


– Sewage generated by houses or runoff from septic tanks into nearby waterways, introduce organic pollutants that can cause eutrophication.

– Fertilizers, herbicides and pesticides used for lawn care can runoff and contaminate the waterway. As with agricultural fertilizers, home fertilizers can lead to the eutrophication of lakes and rivers.

– Improper disposal of hazardous chemicals down the drain introduce toxic materials into to the ecosystem, contaminating the water supplies in a way that can harm aquatic organisms.

– Leaks of oil and antifreeze from a car on a driveway can be washed off by the rain into nearby waterways, polluting it.